Probably Chidori of Persona 3. Gothic, with messed-up priorities, a pessimistic view of other people supported by the chill way in which I treat them. I'm at odds with myself often, and keep it in check by medication and art. Having a crazy witch living inside my head would be pretty boss, too, despite the fact that it'd kill me in the end - I'd rather not live to be old, regardless.
But of course, that's only who suits my personality. If I got to choose, I'd be Rose from The Legend of Dragoon, because living for eleven thousand years, tainted with inhuman power with my only legacy being that of an inexorable monster that ritualistically haunts history would be SO FUN.