Check my gear before taking my comments at their face value.
I can tell you that I am really happy with Sigma. The EX Quality is outstanding, and it is currently the lens that is always on my pocket. I have bought it less than a month ago, so I have yet to take some photo tests and post them.
I did have a thread in this forum about this same subject, and got a lot of positive reviews on the Canon 10-22, as well as the Tokina. I am a Sigma kind of guy, and for the money I went instead for Sigma rather than Canon, it was a toss up (well, the best lens for you is the one that makes you happy, and for me Sigma's metal construction is a ton more comforting that the all plastic construction of the Canon). No lens is clearly better than the other, but Sigma hit the spot for me. (BTW, I did get the EFS lens, no Full Frame Support, but I can live with that, since I will keep one 30D for at least 90k more actuations, and probably even further).
I hope this helps, and I will get some tests photos to post here this evening.
Cheerios,