8mm compared to 11mm? you're seriously going to try to make that a reason to decide between either lens? Haha.
The Tokina is mostly awesome because it's f2.8. Very fast, and damn sharp if you're looking for a high quality wide angle lens.
something like the sigma 8-16mm is variable aperture and slow as shit, you can't use filters on it, and even though it too is very sharp, that f4.5-f5.6 is sloooow if you're trying to use it indoors, where a UWA is very useful.
Not only that, but the Sigma usually goes for 450+
It's worth the extra 50-100 or so for the Tokina.