Here's some things to think about.
1) If there's a main character in a novel that is a villain, what would you like to see in him/her?
2) Would you expect him/her to have a twisted or sad past?
3) Even if he/she is a villain, would you mind him/her showing empathy in some part in the later chapters?
4) Last and least of all, do you like to read a main character that is actually the main villain in the novel?