I own both the Canon 10-22 and the Tokina 11-16. For outside, daytime use there is no comparison - the 10-22 wins all the way.
Do have any shots to back this up? I have used both lenses, but I never had both at the same time. My experience puts the Tokina IQ slightly ahead of the Canon, but either way they are both very good, and I think there is definitely a comparison to be made.