Sexual is by far the best. IMHO it shouldn't be punished more than normal abuse (ie beating someone up). I know way too many girls crying "wow I was raped" and getting rich because of it, when they admit to their friends without any trouble that it was just like normal sex, and they enjoyed it. In fact, I think it's more human than most of the abuses, if not all.
Psychological is the worst, but it needs really, really good planning, and few people are capable of exploiting even 5% of what psychological abuse can do.
Physical abuse is close to the psychological one, but not nearly as dangerous as the psychological one. The only thing is that it's so extremely easy to abuse someone this way. We all can. That's why in total, around the world, physical abuse probably harmed A LOT more people, though I maintain my opinion that psychological one is worse.
Edit: I agree with Fifty, BTW. The question doesn't really make much sense.