I'm honestly unsure...I mean, I would be very situational as a person. My problem with games like Fable and Mass Effect with their morality systems is that, I'm not a total goody good, but I'm not a demonic slayer of mankind either. I'm what may be referred to as an Anti-Hero, atleast for me personally.
I'm always for the side of good, but my methods of bringing good to people can be unorthodox. For example, I'm often considered a cruel, insensitive person. Under certain circumstances, when I mean to be like that, I'm doing because sensitivity in said situation won't solve anything, just cover the problems up.
So I wouldn't be a dark and sadistic hero, but I'd be a hero who's more willing to perform something criminal if it resolves a situation.