I'm going with The Others for now. The Man in Black has proven sneaky and calculating, but The Others I think still have him beat: Brainwashing, indiscriminate murder and maliciousness (the MIB at least is selective of who he slaughters, not to play devil's advocate).
Still 2 episodes left (1 episode and a 2 episode special), so we'll see. I'm guessing that if allowing him to escape the Island causes the world to go to hell (even though there's already plenty of evil in the LOST universe and our own) it means the people brought to the island are supposed to represent humanity.
Extra: Is Jacob supposed to be God, an angel or something else?
Still 2 episodes left (1 episode and a 2 episode special), so we'll see. I'm guessing that if allowing him to escape the Island causes the world to go to hell (even though there's already plenty of evil in the LOST universe and our own) it means the people brought to the island are supposed to represent humanity.
Extra: Is Jacob supposed to be God, an angel or something else?