What makes a perfect villian?

Ok I know that I've been writing a lot for one day, but I'm kinda new to this whole blogging thingy. Ok in most of my books; Talking Cake, Diary of a Lipgloss Addict, and my new book The Tales of fantasogra usually have female villians. I find it very hard to write male villians, and it was expecially hard to write The Talking Cake(it had 4 female villians!)
Ok some background info on The Talking Cake. Ok my sister had written a book called Talking Pie. when my sister was in Kindergarden and she wanted me to jazz it up. So I did, but I just changed the title and a whole lot! The original characters were suppost to be my sister S(abriviated) and I. I then took out S and I's name and put in my main 4 characters names. Which are Claire, Daisy, William(who I feel may not have a real personality in my book), and Trevor( if he were real I would probably date him). Then there my four villians(I made the villians equal to my heroes). They are Carlisa, Minerva, Drisela, and Laverna. Unfortunatly they are common female villian nanes(well Minerva and Laverna are). I totally made Carlisa and Drisela up.

Ok in Diary of a Lipgloss addict, the main villians are a bunch of wild, drug-addicted teenagers who are in a gang. In The Tales of Fantasogra the villians are the government and the Upper class. I noticed that the villian in The Tales of Fantasogra might be the cruelest character I ever written. I mean she's(yes she) is cruel, and she cares only for herself. Though what makes a even better villian? Does a villian just have to be cruel, or is there more. Should I explore her personality deeper, or just keep making her evil. Should I have her turn good in the end, or have her end tragically.
To be evil or to not be evil. That is the question.
-AM