I'm not a big D20 player, but I'd say that most of my characters (both those who have alignments and those from systems where alignments aren't used) tend towards Lawful Evil, or very occasionally Chaotic Evil.
I seem to have picked up a quirk for playing socially predatory personalities, often morally bankrupt people who hypocritically cling to a facade of honour or very public code of behaviour in order to protect themselves socially or maintain the illusion that they're better than the average scum.
There was a time when I played nice or sympathetic characters, but when my mental state got bad I found I tended to attach to them to a degree I found uncomfortable. Nowadays, I find it much more fun to play a character I would hate if they were a real person, so that's what I've always done and where my talent lies. Like I said, it's a quirk.
If the specific game doesn't really allow for evil characters, I tend to jump to the opposite end of the spectrum and play really unrelenting moral zealots (Lawful Good or Lawful Neutral). It's not as cathartic, but I still find it solves the identification problem.