Butt and Malik are quite clearly the best captaincy options that Pakistan have at the moment and have captained competently for their domestic sides. Yes, I am aware that Malik threw a domestic game, which was a mistake, but I think we can all get over that now. He has been reported for chucking, is there a point behind that? Big deal really, so has Muralitharan and he does pretty well for himself. I agree about Butt, he needs to secure a spot in the team first, which shouldn't be too hard for a player of his class.
Mohammad Asif should never be made captain, or vice captain for that matter. Aside from the drugs issue, he is too young and should be concentrating on his bowling. However I don't agree with your opinion about Yousuf, the guy doesn't seem cut out to be a captain, and just because he has been a great servant of Pakistan cricket doesn't mean diddly-squat really, because he isn't good enough to captain an international side.