I like those guys the most.
In my opinion there are three types of villains.
1. The ones who suffer from inferiority complexes, seeking for world domination or revenge, for example. Flat and easy calculatable, just boring but the most common ones.
Examples: 80% of all villains and Sasuke^^
2. The ones who kill for the greater good (e.g. a better world or preventing sth. really bad from happening)
Those are the only ones who are not necessarily flat, however they hardly fit to be called villains.
Examples. Pain, Big Boss, Aoshi Shinamori, Lelouch Lamperouge (You forgot 2 add him)
3. The ones who just enjoy killing / being evil.^^
I have to admit that they are also flat but theyīre not easy calculatable. In addition, those are the only ones who can never be convinced that what they do is wrong. The only thing that would make them stop killing is getting bored by it. And thatīs why I like them the most.
Examples: The Joker, Kid-Buu, Priscilla,
Sorry, canīt think of more right now. ^^