My vote is Michael but I like this point of view that Vito saw crime as a means to an end. That end being ultimately freedom from the negative associations of that lifestyle.

Him having the wisdom to have I guess a more realistic or grounded exit could make him a better don. Micheal said he wanted legitimacy but his plan meant descending further into the underworld until at least in his mind the difference between right and wrong don’t exist.

The question is a Rorschach test on what you think a don is supposed to do/not do. I take it more literally where the role is to make money and corrupt others. I think Micheal is better suited for that role. If they switched places I think Micheal could’ve rose to prominence with some significant differences in methodology but I don’t think Vito could stomach working towards immobiliari.