For me I would say that mine are Hush (Batman Hush), Two-Face (Dark Victory) and Bane (Knightfall). Who are yours?
Ra's al ghul has always been the coolest to me ever since his appearance in batman TAS and he's the only villian that invites batman to kill him, and regularly comes back from the dead. There's nothing cooler than that, and how he calls batman detective. He's my favorite. I like riddler joker two face bane and black mask as well. Black mask is really sick though, even more so than the joker.