Half-and-half. Usually, my characters are slightly insane, dangerous cross-traders or some other unsavory sorts (which I am not), but they pick up my personality traits in the bargain.
My characters will never be the same as me until I roll a character with 18 in every score. Also I tend to play characters with a range of flaws, while the only flaw I have in real life is my humility.
I base my characters on personalities/characters from TV shows, movies or books and extrapolate how that character would react in a fantasy setting interacting in the situation at hand.
All those years of doing theatre and drama didn't go to waste....
My characters are usually how I would be without society's restrictions. I.E., if I see someone hurting someone, my characters would probably just lop the guys head off. In real life, eh, I might stop him, but not so violently.
They tend to be pretty close to me, though more like "me as I want to be" in many cases. I play many physical types (and even cross the gender line now and then) but they tend to be hard working, practical, self-sacrificing early risers who don't complain about discomfort or bad food. So ... maybe not quite like me all the time. Say 60%.
It varies a lot from character to character and there are so many criteria to compare on, but this seemed like the best answer. Every character has some subconscious influence from my self.