If this is a popularity contest, The Beatles win, followed by Elvis.
They've sold double despite their activity lasting more than 3x less than MJ's and the latter having the advantages of the later eras.
OT: None of them deserve the title as King of the music industry because none of them were especially talented. They were all famous because they revolutionized the music industry in their own ways, but none of them were outstanding... above average? Yes. Spectacularly talented? No.
MJ's been the worst for the hype though. Like the others, it was the music produced that made him famous, not talent. His vocals were flimsy, his dancing skills were just "okay" and his performance skills were better than average. There are a plethora of better talents in the East right now, that can do what he did better.
Unfortunately, the best talents are usually overshadowed.