Just purchased the Sigma after a long debate about saving up for the Nikon (business has been slow). Saw the tamron for $700 and thought it was a great deal. Read up on dpreview.com and other places. But when I tested it the colors were a bit off (for my taste). The Sigma was much better ($100 more). I shoot with the D80 and D300 and found the Sigma worked much better. Of course the Nikon would be perfect. Now for the question... Would you choose the Sigma or the Tamron? Why?