Is Elvis the greatest ever?

As an entertainer (i.e. onstage, on TV, live in concert, etc.) the answer is YES.

As a singer (who never allowed his music to be enhanced and whose singing, even while moving around onstage for hours, etc.) the answer is YES.

As a man he had his faults, he was human, but when his life is put in context there is no doubt that inasmuch as a person can be....he was great.