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.