I have read they all wanted to fire Pete Best, but were too cowardly to do it so they put it on Epstein. George Martin had been brought in to produce their records and thought Best couldn't keep time — which was already obviously known by the other band members. There were personality issues as well. I think it was McCartney who said the other three were very artistic and Best was not and that wasn't a good fit.
Ringo was brought in and the one thing he was really good at was keeping time like a metronome. He was also the guy that tried to keep the Beatles together — probably the "nicest" Beatle. McCartney pushed for Ringo to get inducted into the Rock and Roll HOF as a solo act.