Please... put... 56k warning signs on the third one.

Anyways, I like the first one, although the teeth look a little wierd. It's very nicely blended and colored.
The second one, it might be me or his right ear is bigger than his left. It might need some sort of shading as you can barely tell where the head ends.
The third... I like the style, but I don't know much about it so I don't think anything's wrong with it.
I'll say something about the fourth once I get over my fear of large webpages.