Villains

What kind of bad guy do you like in your books?
Obviously it depends on the genre you write, but personally I love the subtle ones.  Ones that you're not quite sure if you like them or not.  The example that comes to mind is Anna Karenina (because I read that book recently!).  I was sympathetic towards her until she left her only child, that she adored, for a man who she was having an affair with.  Then she became unforgivable to me, because how could a mother do that?  In a way, these kind of people are fun to read about because it gives you a little boost, as in, I'm a much better person than this.
In the novel I'm working on, my villain is based on a real life person who portrayed herself in different ways to different people.  From the perspective of certain people, she was not a bad person at all, but there was definitely an ugly side to her character.  That's how it is in real life, and that's what makes it interesting.
What's your opinion?