DingoSeanTokina 11-16 f2.8
Tokina 12-24 f4
Personally I like the 12-24 because of the extra range, and the better matching with 24-70ish zooms (which I find to be far more useful and keep-able than the 17-50 crop zooms).
Both lenses are built in the same shell, and are built to the same quality as each other. the 12-24 has slightly more distortion, and isn't as sharp at F4, but with landscapes or skiing, i'd always be shooting at like f8-f11 anyway, so that's a moot point for a wide angle zoom. It's an easy trade for the extra range of the 12-24. Additionally, the 12-24 tends to be more affordable. So that's pretty nice as well.
Either way. Both are great lenses. Most people on this site drool over the 11-16, and I don't blame them.
Go with what you feel is best for you. Cheers.
Cheers for the help, I'll check them both out