OU. It's true that Blissey is the definition of annoying, but it's definately manageable, especially in a metagame where physical sweepers are dominant. Blissey DOES work really well in Ubers because of the majority of Special sweepers, but as I've told people time and time again, and something that Smogonites just can't understand, just because it does well in a tier, doesn't mean it belongs there. Want proof? Well, Darkrai can do well in OU, and it's in Uber. I could go on forever with examples.