The hopeless romantic in me likes Brutus as my favorite character. He shows all the complexities, weaknesses and vacillation to which humans are prone; he unwillingly betrays his friend, and attempts to justify it, but ultimately regrets it:
Caesar, I killed not thee with half so good a will.
Marc Antony to me is something of a schemer himself, Cassius is a villain, albeit a somewhat noble one. Caesar is a tyrant. There is no vacillation or hesitation in any of their actions. Brutus is a man torn between loyalty and duty, and dies unable to reconcile them. Truly he was "the noblest Roman of them all."