Tough decision...really tough decision. Here's my rankings:
John: Founder of the band, often referred to as the "Chief Beatle", hard-edged vocalist, probably led the Beatles musically through "Help", technically probably the less talented musician of the four (in my opinion), but made up for it in his songwriting.
Sir George: Took a big chance signing them. Who but Sir George could hear the promise they presented from the Decca tapes? Recognized that their personalities would play a part in their success. Figured out that Pete Best sucked goat for half-price as a drummer. Open-minded to their ideas. Taught them how to construct a hit song ("She Loves You", "I Want To Hold Your Hand"). His background in both comedy and classical music was a major plus.
Paul: Best musician in the group, cute as hell, when his lyrics caught up with his melodies - he became John's equal in songwriting, best PR man in the band, knocked the rough edges off of John's harder side, led the Beatles in the later years when John abdicated his leadership, vocally he had the best range and could sing believably in any style.
George and Ringo: The only lead guitarist and drummer the Beatles could ever have wanted to have, in some ways they were inferior to John and Paul - but better to have two underachievers in the band instead of 4 egomaniacs in competition, neither can be listed among the greatest musicians - but they were perfect for the Beatles, when they DID outshine J&P, they did it in a big way on so many levels.
Actually, they are all so close to being MVP's, I say they should all share in the award.