Great comparison site for Canon lenses and their image quality -- both look pretty impressive. I can only personally vouch for the 17-40L: it's a great lens, reasonably sharp stopped down just a little bit, and only has slight barrel distortion and/or vignetting at the wide end/wide open.

Canon EF-S 10-22mm f/3.5-4.5 USM Lens - Canon EF 17-40mm f/4.0 L USM Lens Comparison - ISO 12233 Resolution Chart Results

If you get a chance, I'd try them on whatever body you're using. Even with a 1.6x crop body, the 10-22 will give you only a 35mm equivalent at the long end -- if you're ever taking pictures of people (not big group shots), you're going to need to be very close. Not only will this necessitate having very confident subjects, but you also have to be very careful of significant barrel distortion, especially at the very wide end.