I want to learn martial arts for self defense, what should I look for?

If you are looking for defense against weapons, use Krav Maga.It was designed for defense against weapons. You can also try Ninjutsu. I know a really good knife defense where you can take their weapon while locking them so they cannot move. The bad thing is that unless you know that technique really well, and have practiced it with different people, you might get yourself hurt.