Oh man, that's a tough one , they were all worth 1/4 of the group, each one in his own way. Personally I would say Ringo, because even thougth he was the least talented ,he was the SPECIAL GLUE that held the togeher for so long .
george harrison i like a lot but also john lennon i love in the beatles "while my guitar gentley weeps", lot of george's solo work and john lennon's" mind games"
Before his assassination, I had the pleasure of seeing him and Yoko on the streets of NYC walking around like ordinary local folks unmolested by fans only to be set upon by a crazy person in front of his apartment building. That was fate!
Ringo -> John -> Paul -> George