Elvis was, and always will be. He wasn't called the king for nothing. His music and his movies will keep him living on in our hearts long after all of the others are long forgotten. He was the fountainhead of rock and roll, and all that followed, owe him a debt of gratitude for having paved the way for their successes that came after him.
Michael Jackson because his career lasted longer. Even though The Beatles and Elvis Presley had great hits, Michael's "Thriller" made it REALLLY big. Michael Jackson is also a lot more famous internationally. Michael's dead and he's still very very famous.