Michael's the best simply by way of how he moves. He's technically brilliant. You brought up a good point KOPV in that versatility is one of his great strengths, he isn't limited to any one specific genre, he can pick up and imitate any step or style and do it well on the first try, he isn't good at just one form of dance, he's good in every form, he can do anything. I always say, he's a master of movement and if he were to concentrate on any specific field of dance, he would become the best in that one area.
But the fact that he has this rare combination of speed with precisian/ accuracy, perfect lines, and phenomenal control, he simply moves, in a general sense, overall, better then everyone else. Just in terms of of how he flows from pose to pose, how cleanly he executes the steps, how quickly and easily he goes from one mark to the other. Nobody moves that good, in an overall sense, just in terms of movement. Except Fred Astaire. I think as far as natural ability goes, Michael is the most gifted dancer that's ever lived.