I love boxing, but I don't know if it should be a preferred method of self-defense. Obviously someone trained in boxing can defend themselves, but think of it this way:
-- Most people that are going to give you trouble are going to just start winging punches at your face. Even as a superior boxer, do you really want to get into that with a stranger?
-- Without proper protection, it's incredibly easy to break the tiny bones in your hand on someone knucklehead's skull.
-- When the police show up and this guy's got a black eye and a bloody nose, it's going to be much harder to claim self-defense.
Meanwhile, a takedown can easily subdue a single opponent without much harm to you or your assailant. I also happen to think the muay Thai clinch and the leg kick are both invaluable weapons for self-defense.
This is all just my opinion, of course. In the end, I think the other advice in this thread ("Do what you enjoy doing") is very good.