I have had the the Sigma 17-50 (new) and 18-50 (sh) and to me the 18-50 perfromed better. I had bought the 17-50 from Amazon and sent it back as it was dissapointing (back focussing), I then bought the Tamron 28-75 as previously mentioned.
I havent had the Sigma 17-70 or Nikon 16-85. I believe the new Sigma 17-70 art? gets good reviews and it seems Sigma have upped their QC over the older model. you can also buy a USB dock for the lens for calibration.
The Nikon 16-85 gets good reviews and is also more versatile along with the Sigma 17-70 for that extra reach over the 17-50 or 18-55 lenses.
What you want to watch is you dont get to engulfed in looking at all these lenses and start confusing yourself, it's what I used to do. You need to go to a good camera shop with a good selection and have a play around with different bodies and lenses and see what you think is more suitable.
What I did initially was to buy the cheaper kit lenses with the body and then decide what your preferred shooting lengths are, then buy the faster better lenses. I had the Nikon 18-55 & 55-300 which I sold on ebay and then had a play around with the better lenses and settled on the Tamron 28-75 and 70-300mm. After looking at my images the 28mm starting lerngth was good for me as I rarely shot anything wider.
Yeah and it will save some money. And to be honest my level of photography won't really need the faster lenses yet I guess. Just thought would have been nice to just skip out the kit lens and take 'better' pictures without buying 2 lenses but may aswell do it the sensible way and work out what lens I need properly instead of just grabbing any as such
you got some pretty good advice early on which was to buy the camera (whichever one you decide on) with the kit lens and then as your skill and experience builds up - decide what lenses you need from their and build your collection.. but in the last two pages all you seem to have done is 'decide' what lenses you want (not necessarily need) - without even using the camera!! LOL!.. salesmen love people like you as you're obviously in a hurry to part with your cash. If you;re not careful you'll end up with kit you won't even use that much.