David Haas , Mar 08, 2011; 06:20 p.m.
Shooting wise - I prefer the Sigma in the common focal lengths over the Tamron. But the differences are so small that to me they are meaningless.
Build wise - the Sigma is built like a tank - and the Tamron is built like a ...hmmm.
If I were shooting all day - the Sigma would definitely build up arm muscles. I don't even notice that the Tamron is on camera.