It was close, but I chose Stefano. He is just plain evil, although he has been a bit of a pussycat around Kate. The only time he really shows deep feelings is for his children.
I have always looked at EJ as a Stefano in training. The thing about EJ is that he appears to be wishy-washy. He can be cold as ice, and then he can also show his feelings for Nicole. I never know exactly how to feel about him.
I don't know enough about Ian yet, but up to now he seems pretty cold.