My favorite villain is one that truly believes he is right. It is just that his morality is so twisted, he is doing terrible things for perfectly justifiable reasons in his own mind. He sees himself as the hero.
TV: Andrew Scott's Moriarty in Sherlock. Absolutely hilarious and terrifying. Truly sadistic and crazy, and most importantly, brilliant.
Movies: Khan in Star Trek. Both versions, in The Wrath of Khan
and Into Darkness
. In spoiler tags. just in case,
Also, Ra's al Ghul in print and film for his worthy attempts at world balance and purification. Unfortunately that came with death for millions, but "the needs of the many outweigh the needs of the few." Oh wait...too many crossovers.
Gaming: Revan, because he was an almost counterproductive Sith Lord, leaving the structure of a galaxy in place while simultaneously ruining it. A very complicated villain/hero, about whom I would read dozens of books.