Between Simon and David for me, but I chose David. Yes, he is a little questionable sometimes, but he is the most fun.
Amanda's okay - though this is kind of the only way she's famous anymore.
Alesha I don't like. She adds nothing to the show.
Simon I like, though I don't like the way he claims to "not like" certain acts (joke acts) though ends up putting them into the semi finals so he can A) make a mockery out of them and B) get better ratings.