I voted with Sean Sherk. Sherk has a wider range of take down abilities. Also for size vs takedown he is able to lift and deal with getting people that are bigger than him to the ground. Although he often uses the same takedown, I've seen him use a lot of different ones that some of the others have not. I think he sets himself up better for the takedowns and uses lead off combos to set himself up for the clinches rather than bull rushing his opponent (for the most part...I have seen him bull rush a few people).
Evens takedowns are more like watching an arm wrestling match.
Kos has "A" good takedown and that's it. He can't set himself up for them and when he gets them they are all done either by his opponent forcing a clinch or he performs a bull rush. He has steller speed and strength but lacks experience.
Hughes has a good takekdowns but that's not really his forte any more. I think he works better now once he's on the ground. I think he's actually become insecure with his ability to get to the clinch for the takedown after watching his fights with BJ and GSP.