I am absolutly in love with my Tokina 12-24. Now in all fairness I have heard favorable reviews for the other 2 lenses your talking about as well. The Tokina almost never leaves my camera.
Here are a few shots from it:
I see it as one of the strongest investments I have made in my landscape photography.
It does pretty nice duty as a group shot lens for weddings as well, and with the constant f/4 and you can actually use filters on it...it's quite a lens. Only issue is if you have 35mm...its a DX format only lens.
Hope this helps...if you have any questions...ask away!