Well, my favorite character to write is Draco, and I think it's because I can make him work in just about any situation. Also, it's easy to get into his character for me. He's one of those characters that can say what he thinks--and therefore, whatever the writer wants him to think, he can say. He can be withdrawn and snarky, he can be an absolute slut and proposition Harry or Ron, he can be a drama queen diva and throw a flaming hissy fit, and hardly anyone is going to look at any of that and claim that it's out of character. In our everyday RLs, we can't get away with acting like that or talking like that, but this character can. This makes him enormously fun to work with.

In the books, however, I think my favorite characters would be Luna, the twins, and Snape. They crack me up ;D