It has been said that an antagonist in a story should be 3 parts bad and 1 part good, and that a protagonist should be 3 parts good and 1 part bad. That's useful. Purely bad characters are frequently too uni-dimensional to relate to. That doesn't mean that there aren't people in the world who have no redeeming qualities, but their thin little lives are seldom interesting or compelling to the reader. Fictional worlds can live without them completely.
In my previous post I linked to another blog because their villains list was so in tune with my own. In particular, the most compelling villain to me is from the Outlander series by Diana Gabaldon. Jack Randall is a horrible sadistic monster, but he will make great sacrifices for family.
In my upcoming novel, A Swift Taste of Red, the villain is the scion of an evil family, and is loyal to his family, while at the same time having a complete disregard for any other member of the human race. He is charming, brilliant, gifted, and very, very bad. That's my kind of villain.
P.S. New facebook page link- www.facebook.com/authorgabrielleback.