technically, george, for sure, he was a great lead guitarist.
Datz rite; people often make fun of George and dismiss him because he didn't have the chops of Eric Clapton or Jimmy Page. But his solo work on Abbbey Road is some of the most lyrical lead guitar work ever done. And the fury of the Revolver songs. He just wasn't flashy, but so aren't a lot of great players, in all the idioms.
I had to vote for George but I must mention Ringo. Everything I siad about George also goes for Ringo. You can't have a great Rock or Jazz band without a great drummer, and Ringo was/is one of the great groovemasters of the drum set. Stylistically he is usually the same, but that's one of the things that made the band great and unique, IMO. Through the drums he gives the band it's unique sonic and rythmic signature...