I've had the luxury to be at everyone of the aforementioned artist concerts.
Michael, too me gives the best spectacle performance all the while maintaining some semblance of a singing voice.
Prince, gives an awesome performance, less on spectacle or vocals more on dramatization(acting out) as well as musicianship, he is unmatched.
R. Kelly, great vocal performance sounds close to his studio music. Talented singer song writer who doesn't do a lot of dancing around just full on vocals.
Usher, is good in an also ran type of performance. He's doing what Michael's was doing decades earlier to a lessor degree. He doesn't match the energy or spectacle of Michael.