r1ch wrote in post #7782567
Another reason to get the Tokina is compatability. It will work on a FF camera that you may purchase in the future. You would crop out what you don't want. The Canon limits you to only a crop sensor camera. Always look to how you might use your lens in the future, the Canon cannot be used on a 5d but the Tokina or the Sigma (I believe) work on a FF and at the 15-16mm angles does not even have black vignette.
I feel that this is VERY bad advice.
Buy what you can use NOW. Lenses generally hold value quite well, and can be sold to fund lens upgrades IF you go full frame.
Had I listened to similar advice, I never would have gotten my 10-22, and would have the Sigma 12-24, missing out on the extra 2mm on the wide end. At the start, I was planning on going FF with my next camera (and was waiting, like everyone else, for the 5D mkII). As of right now, I do not see myself upgrading to FF for at least 2 years (although, that falls under the category of "The best laid plans of mice and men..."). 3 years is a lot to go without 10mm as I am practically always there.
OP: Everyone has a favorite UWA. The Tokina 11-16, Sigma 10-20, and Canon 10-22 all perform very well. They also offer a little something different (from focal length, to aperture, to price). Find the one that fits best for you, and go for it.