Was looking at this lens for a good walk around lens and overall general lens to stay on the camera most of the time. Anyone have the lens and care to comment good or bad? It will go on a Nikon D7000 if that has any bearing.
Have you considered a 24-70 2.8 lens? Tamron makes one that I really have fallen in love with. You give up a bit on the wide end but it's nice to have that extra reach still at 2.8. The Tamron version also has VC.
The reviews on the 17-70 seem to trend better than the 17-50. I haven't tried the 17-50 though so I can't give you a first hand impression.
I have tried the Tamron 24-70 f/2.8 but only on a full frame (D610). It is fantastic and performed better for me than the Nikon. I have never tried it on a crop sensor. If you see a full frame body in your future then the Tamron is worth a look.
I have the sigma 17-50 f2.8 and it basically stays on my camera. Love the sharpness and colour rendition. But I have no experience of the 17-70 or 24-70.
I expect the reality is, whichever you go for, you will get on well with.
Personally I'd go for the Tamron 17-50mm f/2.8 VC, it's sharper, has less distortion, and controls chromatic aberrations better than the either the Sigma 17-50 or 17-70mm.
That extra 20mm in zoom isn't worth the drop in IQ.
I have the Tamron 17-50 2.8 and the precursor to the 24-70 f2.8 the Sigma 28-70 f2.8. Each are almost exclusively mounted to their respective cameras. I prefer the 28-70 for the extra reach (as a walkaround) however when I need to go a little wider I will grab the camera with the 17-50 on it. Both lenses render very good images and are well worth the $. With the Tamron I do find that I have to use a +1 EV (Pentax camera) to get the exposure I want.
You can't really generalize. You need to seek out reviews of specific lenses. In some cases Sigma is better, in others Tamron is.
If you are considering the 17-50 2.8 lens, I've always heard the Tamron is sharper, at least in the unstabilized version. Other lenses, I have heard Sigma is better.
Well it looks as if I have narrowed it down to the Sigma 17-50, F2.8. According to both photozone.de and DxOMark, when mounted on my camera, it has the best ratings between it and the Tamron.