With UWA lenses, I want to use ND/polarizer filters. I don't know if that's a consideration for you, but something to think about. The Canon 10-22 is sharper in the corners than my 17-40 is on full frame. It's a great lens. I also had the variable sigma 10-20, and it was an excellent lens too.
It will probably come down to the extra on the wide end vs 77mm filter usage...
