I've just bought the Tamron 70-200 2.8 VC.
While not as good as the Canon it's exceptionally close especially in image quality. The Tamron image isn't soft at 2.8 like the Sigma is.
If you don't need 2.8 then none of these lenses are the answer, get the canon f4 IS for the weight saving, the 2.8s are all heavy.

The Tamron is way too close to the Canon for me to spend double the price on the Canon. There is a huge range in prices for the Tamron lens, but it can be had for $1300 for Australian stock from a walk in shop. Not sure about forum rules for posting links.

The only thing I don't like is the swapped zoom and focus rings, I'd rather have zoom at the back. It's easily overcome by using the tripod stand in my palm and can zoom without problem.

Take your own camera body into the shop and try the lenses. Take it home and have a good look at the images before buying.