I have recently purchased a Tamron 17-50mm f2.8 VC, and subsequently a Nikkor 17-55mm f2.8.
I think the Tamron is a very sharp lens in its own right, especially when you use a smaller aperture. At the largest aperture of f2.8, however, I think the Tamron is a bit softer when compared to the Nikkor counterpart. Also, Tamron is a bit slower in a low light situation and a bit noisier with the VC. Furthermore, Tamron doesn’t appear to be weather sealed, but the Nikkor is. The Tamron has a VC, while the Nikkor doesn’t.
If you don’t plan to spend $1400 or so for a lens but are still looking for something sharp and fast, Tamron would be the perfect affordable substitute. However, if budget is not an issue, and you want to be able to use the largest aperture in a low light condition and still producing the sharpest images, and that weather seal is important to you, then Nikkor would be recommended.
I decided to keep both lenses, though the Tamron will be used primarily by my wife with her Nikon D90 due to the lighter weight, while I will use the Nikkor with my Nikon D300S.
Tamron AF 17 50mm | taaag