Evil sure as hell levels faster. I started my evil alt a week later than Tal, and he's already a friggin' Myrmidon. Then again, that could have something to do with the XP bonus that comes from the damage bonus of being in the OS. Other than that, the ability to wantonly kill is the tradeoff. That's the balance. Good guys are much more powerful than evil guys, but they have to work harder to find targets so that they don't lose morality and get their powers taken away. Evil guys have no such disability.
Also, just to scare you guys: There are currently about two hundred OS members in their stronghold. Of that number, I count seventeen who are below level 10...This place is an XP farm waiting to happen...