If there is any mission I have as a writer it is to attack the Appalachian stereotype. Whether it is the victimized hillbilly or the evil sheriff in the black hat, we've all seen them on TV or encountered them in books too many times. The villians, in particular, are important because utlimately they drive the story. If the villians are simply evil, then they are interesting for about twenty minutes and the reader figures them out fairly quickly. Villians who struggle with their own actions are ones that interest me.
Internal conflict makes villians far more untrustworthy than simple evilness.
I don't know what decisions they're going to make. Having a complex antagonist also adds a dimension of conflict for the protagonist as well. Justice and retribution have a different meaning in fiction and it is the main character who has to dish it out. It's easy to send a villian to jail, but far more interesting to read about a comeuppance that strikes the character to their very core. And in college Gothic literature class, I made the argument that Dracula was simply trying to survive and Van Helsing's gang were the tormentors.