My opinion is that they're both superb wide angle optics. Granted, the 11-22 is one small zoom and Canon broke the mold when they made that one - it's that good.
But I also use (with an adapter) the EF-S 10-18, a highly inexpensive EF-S lens that I find exceptionally sharp. I keep one attached to an older M2 where it blends perfectly and the results I get from that combo are outstanding. In fact, I love that 10-18 so much that I purchased a Fringer EF to FX adapter and a 2nd copy of that lens, and use it on my Fuji X cameras because of the sharpness of the lens (with all electronic functions, AF, and IBIS completely compatible). My two copies are just that good!
But in getting back to the 11-22, you can't wrong on this deal - unless, of course, you get a bad copy. But with the 11-22, Canon has been really good about keeping great IQ consistency across various copies. Highly recommended.