If you specifically need a f/2.8 go the Tokina, otherwise I don't think it makes much of a difference. I went with the Sigma 10-20 because it was sharp and the least expensive. I am not typically a wide angle person, so I saw no reason to pay more (for me). When I do use one, I typically stop down. Again - stopped down I would think it makes little difference on the choice.
You're a smart man, Jim! Sounds like the Sig 10-20 will work for me as well.
I can save some dough on going with the Sigma and use the money I save to go for a 24-105L lens for my walk around lens. May even get rid of my 18-135 to help me with the cost for the L lens.
Thanks again for your help everyone! Just like to talk things through and get people's perspective before going forward on a purchase like this!