My favorite character is Kimbley. I've always had a sweet spot for villains and otherwise scheming characters, especially the cool and collected ones. Kimbley is clearly very smart and strategic, and I like that he follows his own goals, not anyone else's. He's in it for the lulz, legit. There is no Freudian excuse to make him do what he does, he has no real redeeming qualities that would ever make him a 'good guy'; he is just a villain, and an individual, at that. I definitely like him the most in the manga. Being a psychology geek, his mindset just fascinates me to no end.
Ling, Greed (both) and Riza follow closely. I love almost all of the characters, though! xD