Im still looking into buying a dslr.
OK, well on the research front, I can understand coming here, as the amount of technical jargon, and pontification on finer points of performance is utterly mind bludy boggling! - coming here is probably NOT going to make it any simpler... quite the converse!
1/ WHY do you want a digital SLR?
2/ Why do you THINK that the sensor size is important...... TO YOU?
Camera... light tight box... takes pictures... that's it. the bottom line.
Good photographers take good pictures... better cameras merely help them. You do NOT get 'better' pictures from buying a better camera; and when it comes to SLR's... odds are that you wont get any more better pictures than with a point and press compact, in fact probably less!
SLR's are big and bulky.... you have to make conscious effort to lug one about, so are less inclined to slip it in your pocket and shoot stuff with it, like you would a compact.
Next, they are both-hands operation; zooms aren't motor driven by a thumb switch by the shutter button; they have a ring round the lens; so you have to have one hand on the lens and one on the camera... it's not something you can swing around with abandon, and use one handed hanging onto a fair ground ride as you go, kind of thing... takes more deliberate effort.
So, before we even get to the question of all the fif-faff and wonderment of all the possible permutations of settings and menus and automatic program modes, manual over rides and adjustments, semi-auto-modes, programmable function keys, focus options, stabilisation optopns, and fully manual modes.... that offer a whole PLETHORA of extra opportunity to eff up.... chances are you will have missed 2/3 of your photo-opportunities because either:-
1/ You don't have the camera with you
2/ You haven't got a hand free to get the camera out
3/ You have got the camera, got both hands on it.... but... hang on, what button do I need to press first?!?!?!?
SLR cameras are wonderful bits of kit, IF you know what they can do, and if some of that is useful to you, and IF you know enough to make use of it.
Now; fact that you are asking the question, Full-Frame or crop, implies you aren't all that clued up as to what the differences are, but have had some-one who might know a bit more about it than you do suggest that Full-Frame cameras are 'better' some-how, and possibly, in fact probably if they were stood next to a cash register, implying that IF you bought a crop-sensor camera... you would soon 'grow out of it' and want to 'upgrade' to a Full-Frame camera.
OK... lets take this back to basics; WHAT does a full-Frame camera do for you?
And I'm going to talk film. Sorry. BUT, just been scanning some tiny TINY negatives taken with a Minox C Sub-miniature Spy Camera some years ago. Its the camera Sean Connery had in James bond to take pictures of 'Top-Secret' documents..... about the size of a Dunhill Lighter... takes pictures on a negative approximately 8x10mm; (just a little larger than the smallest sensors used in camera-phones and the like) this is about as little as film frames ever got. Its approximately 1/12 the area of a 35mm negative that is the same size, 24x36mm as a 'Full-Frame' Digital camera sensor. Which in turn is about 1/4 the area of the smallest 'Medium-Format' or 120 roll-film frame that is 45x60mm, and goes up from there.
Now; the old adage was that bigger is better. Bigger area of film you expose, better your image quality..... is LIKELY to be... because it NOT the only variable by a long way.
But; bigger area of film you have, more light you are going to 'capture'. You'll need bigger lenses do get it... but you get a good leverage effect; and detail in your scene will be spread over more film.
On Film, image was made by a chrystal of silver halide catchjing a few photons, that made it turn black or part black.... more film you have, more chyrystals you can fit on it... so if I shot medium format instead of 35mm, four-times the image area, I've got four times the chrystals, and each one can turn a different shade of grey, where on my smaller format film, I only have one, that can only go one shade.... so you can 'resolve' more fine detail and more subtle contrast changes.
Translating that to DIGITAL, is not quite so straight-forward; because you have sensor size AND you have pixel count. I have a Nikon D3200, it has a crop sensor camera with 24Mpix pixel count. There are Full-Frame sensor cameras with about half the Pixel count... this suggests then that pixel count might be more important than frame-size.. after all, the pixels are like the halide chrystals, so if you have more of them, you can get the finer detail and gradiations you would have got with bigger bits of film... but as you have probably guessed, its not THAT simple!
No; if you have a crop sensor camera; that has a sensor, aprox 16mmx24mm, about half the area of a full-frame sensor, 24x36mm. Now, you take an exposure reading, that is measuring light 'Brightness' or 'intensity', in mechanical terms its like 'pressure'; its NOT an actual number of 'stuff', its a ratio... whats the pressure in your car tyres? 28Psi? Pounds PER square inch... how many actual pounds of force your tyres are subjected to depends on how big they are, because its not an actual commodity, its a ratio you are measuring. Understand THAT and you can go a long way in this business; an awful lot of stuff is understanding ratios and proportions, not physical 'stuff'...
OK... so... you have a light meter reading telling you how bright your scene is, for want of a better expression, 'the photons per square inch' light pressure.
Now, you open the shutter and let that 'pressure' fall on your film, or your sensor.... umpety photons per square inch... and your camera settings are all proportions reckoned to give the same 'exposure'.... in film terms, enough photons per halide chrystal to tickle it to an appropriate shade of grey; in pixel terms, enough photons to charge up a 'Charge-Coupled-Device' to a level that the cameras brain can measure as a value between, 0 and 255 (or something of that order)... to do the same thing by maths... assign a value to tell a screen how grey to display a dot!
SO.... bigger your sensor... more photons its going to catch.... meanwhile, fewer pixel receptors its divided into, more photon's each pixel receptor is going to get.
NOW... we get deep into the mechanics of elec-trickery here, because a CCD delivers its grayness value from the computer sampling each receptor, and counting, basically how many photons it's caught; but the number is normally so tiny, that the electrics have to 'amplify' the signal before it can make any meaningful measurement.... reversing the analogy to film, this is like the chemical processing, 'developing' or boosting the 'latent' image captured on the film, where the actual number of photons tickling individual halide chyrstals wasn't enough to make them darken up enough to see with the naked eye... However... point is, that the bigger the CCD sensor, and the fewer pixel receptors its divided into, the more photons from your scene each receptors is going to get, the less amplification the electrickery has to do to count them, and get a grayness value... and the more accurate that value is going to be.
So... for the same pixel count; if we have a smaller sensor, we will need to use more amplification to measure levels, and are probably not going to measure them as accurately.
But that is almost our LAST worry... we have to get the light TO the sensor first... and we are grabbing it with a lens. A lens by defanition is a device that allows light to pass through it, but in some way 'distorts' or deflects the lights passage.
Drive down a road on a bright sunny afternoon.... pass parked cars? Each time you pass one, you get a flash of 'glare' as light hitting the curved winscreen is NOT passed through the glass, but reflected... at you, so you dont see that poor dolt on a motorbike.... eeek! (Sorry, I'm a biker! I'll use any aportunity of analogy I can to raise awareness of 'Think-Bike'!)...
So, first off.. you wont ever get ALL the light that even reaches your lens coming through the glass; then what does get through is going to get bent, and we hope, and if the lens is any good, it will get projected onto our sensor, where it will form a representative image.
Now, lets point the (crop-Sensor) camera at a subject; lets pick something of know sort of size; say a car. Its about five meters long, about one and a half tall. And we take the light reflected from that car, and put it on a sensor... 16mm tall by 24mm wide... for the sake of argument... lets give it a scale ratio of 4mm per meter.. so our 1.5m tall car occupies 6mm of the sensor height and its 5m length occupies 20mm of sensor width.
If we framed that same scene of a car, with a full-frame camera? Well, the sensor is 24mm tall by 36mm long.... it's aprox 50% bigger in either direction... SO occupying the same relative area of our frame, the image of our car is now 9mm of height and 30mm of length, a scale ratio of 6mm per m instead of 4.
So we dont have to bend so much light AS sharply to fit it on the sensor.
This makes the larger 'format' or larger sensor size more 'tolerant' of lenses that aren't 'quite' as accurate or precise... more room you have to make your captured image, more room you have for error, or innacuracy.
BACK to my Minox. In 1970 it was a very expensive bit of kit, a marvel of precision engineering, that COULD make images on that tiny bit of film 'as good'... well... as I don't know a Russian Zenith 35mm SLR or maybe a Cheap folding bellows 120 roll film camera.... but it did it DESPITE the negative size, rather than because of it. Sensible people bought 35mm or 120 cameras because they did the same job, a damn site more cheaply, or, using more expensive lenses, could get much 'better' quality for the same money.
Same deal with Modern Digital cameras. They are a SYSTEM, and only ever as good as the weakest link.
And the sum of the parts, is dependent NOT on one 'star' feature, but everything working well TOGETHER. Same as a finely tuned car engine, or a well rehersed band.
A great sensor, is worth bludger all, if its getting light from a crap lens. A great lens is worth bludger all if the sensor cant make sense of what the lens is showing it; brilliant electronics in the camera metering exposure amazingly accurately, is of little worth if the thing ent focused on what you want it to be!
And right here, right now... WHATEVER SLR you chose.... chances are, that in the 'system'.... YOU are going to be the weakest link!
So... back to merits of sensor size... you have the sensor size AND you have pixel count.
Big sensor, on its own, is not going to give 'better' results than a smaller one; higher pixel count, isn't on its own going to give 'better' results than a smaller one... you need everything 'optimised' to work with what you got.
And by and large, full-frame cameras tend to be the more expensive; they tend to be aimed more at people that know more about what they are doing, and are optimised to give a more experienced user more 'control' and versatility over their photo-taking, than crop-sensor cameras that are more often optimised for the keener consumer and hobby user, and generally built down to a lower price.
The more expensive Full-Frame cameras will also tend to take more expensive lenses, as the people who buy them generally wont be buying a more expensive camera to utilise the advantage of the larger sensors error tolerence to use lower quality lenses; they will want lenses that exploit that larger sensors ability to deliver higher image quality.
So, buying in to the Full-Frame system.... you will more likely spend more money to get a camera that is probably harder to use and learn to use, and has an image quality 'potential' an awful lot higher than you are likely to be able to exploit for an AWFUL long while.
Really? Man in the shop said most customers want to trade in thier crop sensor cameras after about a year as they have out-grown them....
Yeah. He would wouldn't he? And there ARE an awful lot of folk who do truly believe that so much of photography is in the kit, and that better cameras MUCH mean better photos....
BUT... bottom line; UNLESS you have some pretty demanding needs from your camera... you probably wont ever 'exploit' a fraction of what ANY SLR might do for you, let alone use it that hard, that often.
I've been 'in' to photography over quarter of a century; and I have taken more photo's, and often more of the 'better' photo's with the little 35mm Compact I got for my birthday when I was TEN!
Last ten years, I have not even bothered with a digital SLR.... I have used cheap and crappy digi-compacts for 99% of my photo-taking....
First Digital Compact I bought? 2003, a Jenopic 1.4Mpix compact..... they put 'better' cameras into smart-phones these days.... YET, 99% of the photo's I ever take are screen-displayed, not printed. As such, even from THAT low level little device, everything has to be re-sized DOWN from camera resolution to the sub 1Mpix of web-distribution / screen display resolution... which is STILL 'adequete' to make A4 sized prints!
It is very very easy to be 'over-sold' cameras, and to be bombarded by techno-baffle, and convinced that the tiny differences in technology are so HUGELY important to your photo-taking that all these expensive features go from being a 'that's nice' to 'must have'... its called good marketing.
But Better photographers take better photo's.... better cameras MAY, occasionally help them...
Which brings us back full circle, and the answer is... if you have to ask... you cant afford it.... oooh... no... well... MAYBE.... but, what was it? Ah that's right.... If you have to ask... you probably don't need it.
Start over; you have probably got in over your head, and romped ahead with an enthusiasm far in excess of your expertise.
First Digital SLR... DO you really NEED an SLR? Do you really WANT one? Could you get more out of it than a point and press or better bridge camera if you did?
For the most part, all they offer is the potential to use a wider range of expensive interchangeable lenses; and for most people, they never go outside the range of wide or telephoto you get built in, in many bridge or compact cameras anyway.
They usually offer a higher degree of manual over-ride or fully manual user settings; which IF you know your exposure triangle from a Dairly Lee triangle MIGHT occassionally be useful.
They may work in a wider range of shooting scenario's; such as extreme low light; or for fast action photography; They MIGHT offer a few extra opportunities for more 'creative' photography and 'in camera' special effects...
But only if you have the need or desire to shoot more challenging subjects, or the imagination, creativity, desire and know how to bet more artistic in your photography.
If you think that this is sort of thing may be where you want to go in your photography.... then a Digi SLR might be useful in letting you start developing the know-how to use one and exploit the possibilities it offers....
BUT... straight off the stops? You would almost certainly be better off with an 'entry' camera designed for a Newby, with Newby Freindly features, and like as not a crop-sensor. And it is unlikely, that even if you DO progress enthusiastically with it, and explore the opportunities it opens up for you, that it will be the weakest link in your photography for a very long time, and that you reach the point that you HAVE to upgrade to full-frame, because the cameras potential image quality is letting down YOUR skill!
If you have to ask... you probably dont need it, you probably cant afford it.
Used to spend my weekends as a kid helping out as a mechanic for people racing cars or motorbikes... old mechanics addage when asked "What changes should I make to make this bike/car go faster?".... fit a better Driver/Rider!
Starting out; thats where you are at, and its likely to be a long while before the biggest improvements to your 'photo-taking-system' is going to be a new camera not a better photographer.
Keep it simple. Start at the beginning. Work your way through the learning process. As you do so, what is more of less useful to you, will be learned.