Well it's a real hard question but I have to go with John, but hey every Beatle had it's time, like Paul is well known for Love songs and hits like Here There Everywhere, Hey Jude, I Want To Hold Your Hand etc
John for Complex lyrics and truth, George didn't get much recognition but he wrote quite Impressive and Decent songs like Something, I need you, Long,Long,Long etc 
and Ringo he did nothing =P
In a timeline it would be:
1962-1964 Lennon-McCartney
1965-1966 Lennon
1967-1968 Lennon-McCartney ...