Paul McCartney with or without The Beatles. He had a genius for melody, his songs were refined by Lennon and were enhanced by the group. Band On the Run is the best album The Beatles never made and the rest of the Wings material is pretty good. After Wings, McCartney's albums are frustrating because they need either The Beatles or Denny and Linda.
George Harrison showed a lot of potential for solo success with The Beatles, but his albums were disappointing, probably because he needed Paul McCartney's influence. McCartney has said that his favourite track on Abbey Road is Harrison's Something, yet Harrison did not record another Something after the final split. Ringo Starr's albums were interesting, but not really great. He was an innovative drummer and should've joined another band like Badfinger. John Lennon was distracted by the musically inferior Yoko Ono, who had less musical talent than me! The only Lennon solo track that I ever liked was, I think, called Losing You with Cheap Trick (?). The Rock 'n' Roll covers were, like Ringo's material, interesting, but a backward step. His poetry is, unsurprisingly, excellent.
George Martin produced the wonderful America and the capricious Jeff Beck. Geoff Emerick took his outstanding engineering skills to technical bands like Roxy Music and Camel.