For 3rd party lenses they are great. Exactly which one are you looking at? I stay away from them because I don't like their build quality. It seems plasticy compared to tokina or sigma.
my friend uses a Tamron 11-22 I think? pretty decent lens, but I liked my other friends Sigma 10-20 better. That's my only hands on experience with them.
Sigma it is then! Thanks everyone for the responses!
I was looking at the 28-300mm but I heard you can get a lot of distortion with a lens with such a large range. I was looking at the tamron version because it comes with the anti-shake feature. The same sigma does not have it.