These were the other two lenses I tried before settling on the Tamron, and was more impressed with the Tokina over the Sigma as well. The Sigma didn't do too bad all things considered, but Tokina has the edge, not to mention build quality. Tokina still tends to use metal on the body of the lens in place of plastic, which makes them bigger and heavier, but also a lot more durable. I have a manual focus Tokina on my Minolta 35mm camera that is a really sweet lens. Too bad it never gets used anymore!
On a sidenote, I clicked his link that goes to the Plastic Wonder test shots, and was surprised by two things. First is that the 50 1.8 is sharper at 1.8 than the other lenses were at f4, and that it peaked at about f4 for it's sharpest aperture edge to edge, with f5.6 not far behind. I would have expected f8 or so for it's peak sharpness.