Daniel Negreanu. That guy is an animal... Most pros can read players pretty well, but Daniel seems to know what his opponent has (exactly) in every heads up play. I like Hellmuth, too, but only because it's fun to watch him have a meltdown.
Phil Ivey is my favorite to watch. Gus Hansen would be second because that guy is just crazy. Hellmuth is cool when he is acting like a dick, other than that hes just kinda a whiner.
Phil Ivey is awesome as well, probably my top. I also like Hellmuth, like everyone else, because it's fun to watch and see what he's going to do or say.