My vote goes for the sigma 10-20 F4-5.6. Best bang for the buck. Feels rock solid in terms of built over the other 2 rivals. Canon 10-22 was out due to budget constraint.
Between Toki 11-16 and Sigma 10-20, the sharpness looks comparable. Having visited the forums and flickr discussion groups for these 2 lens, some pics appear soft while some are pin sharp. Tough call.
So I ended up with the sigma and it has served me well. I do not need f2.8 for landscape shots. Plus the difference in price left me with some change for a good filter.
There are a few threads for these lenses in the sigma/tamron/tokina equipment. You should take a look.