Is capoeira or kickboxing better for self-defense?

Depends on you: As with most martial arts, the moves and forms practiced are self defense based; however, it doesn't matter what moves there are, it's important that you perfect the move and can execute it at the appropriate time. There are fantastic moves in both capoeira and kickboxing. “fear not the man who has practiced 10, 000 kicks once, but...The man who has practiced one kick 10, 000 times.” - bruce lee.

Neither: That's not to say that neither of them can be USED in self defense, these classes will teach you to kick and punch, but if you want to take something for self defense, you should look for a Krav Maga, Jeet Kune Do or similar Close Quarters Combat type training. These will train you to attack the eyes, throat, groin etc. They also teach skills to escape chokes, knife defense etc for self defense.