Which MF Fraggle? hmm how long is a piece of string?
As discussed above there are a number of formats:
645 has the same image layout as the 35mm (rectangle) which some people prefer. The main one is the Mamiya 1000 series, loads about and have good range of lenses and I think they come with metering heads (center weighted meter, no evalutive metering system here)
Other than that you have the Contax machine, great bit of kit but they hold the prices very well and are getting harder to find on the used market.
Hasselblad also do a 645 machine with their H Series. Again fantastic and every thing a photographer wants, IF you have a deep enough wallet.
6x6 the traditional photographers camera, but some people find a square format difficult to use. I don't I love it for everything.
If you are looking at a budget system and you want quality, then the Mamiya 330 series (go for the later F or S ones) is a very good buy. They are twin lens, view through the top exposue with the bottom lens, and have a range of lenes. The couple of flaws with theses cameras are:
Tricky to use filters espically grads and polorizers, but not impossible
Go in close: because of the two lenes you will have to do the old parrallex correction (this can be solved by getting a 'porrofinder' I think it is called) so you have to move the whole camera up to correct it.
Advatages. Tottally mechanical no batteries and because to do not have a mirror slap very quiet to use. Also sync at all flash speeds.
Hasselblads you have the mechanical 500 series and then the electronic 2000 series. These have built a fine reputation over the years and have great lenese. However you will have to pay extra for this as again they hold there prices well on the used market. But their system will allow you to take pictures from the bottom of the ocean to the moon.
They do have some handleing quirks especially with the loading of film in the 500 series (Google it).
Bronica SQ series. These are a Japanese copy of the Hasselblads (why not copy a winning formular) and if you go for one of these I would deffinatly recommend getting a SQAi (last of them easier to do long exposre on). All of the SQ series are electronic machines and will sync flash at any speed.
Again they have a good selection of lens to cover most picture taking situations.
You can get some bargins if you are prepared to hunt and wait on Ebay.
6x7 The recoqnised winner here is the Mamiya 67. Again this uses a rectangle and I believe has the ideal format. The big advantage it has is it revolving back, so you can switch from protrait to landscape with out taking the machine off the tripod. I suppose the only down side to it is its weight, being 5lb you better have a good camera bag and shoulder to carry it. But the quility of the images is superb.
I have used MF cameras on and off over the last 20 years and if you are not doing it for professional reasons then there is very little if any thing to say one machine has better image quaility than the other (only size 6x6 is bigger than 645, 6x7 is bigger than them all).
They do slow you down you need to learn how to see the image, even learn to use a hand held meter (great fun get a Weston Master V, no batteries
).
There are no zooms (well not quite true some of the 645 kit has them) and the lens are usually slower and the max speed of most of the cameras is 1/500.
But they are great hope this help abit Fraggle and keep us posted on what you get.