Well there are so many, it's hard to try ranking them in any way.
Definitely Aretha Franklin would be in the top 10, and so would Stevie Wonder.
Others I would suggest are Charlie Parker, Ella Fitzgerald, maybe Herbie Hancock or Charles Mingus would be up there... Maybe Busta Rhymes could be up there...
I mean, you could put together a list of a couple of hundred great black musical artists, and then subjectively narrow them down based on what you like... but it's hard to make a comparison between, say, Bob Marley and Miles Davis, they're like apples and oranges.
Michael Jackson? Maybe. Putting aside all of his weirdness and the allegations against him, I would say that he made some great music right up to the Thriller album, I personally am not all that moved by anything he did after that. He was a great dancer and performer, granted, but we're talking about musicianship. He was good at that too, but I think there were better.