I guess there is a consensus that George Martin was a great influence, a great technical mentor and a great channel to their creativity, let alone his musical contributions. The Beatles were also produced by Glyns Johns and Martin's assistant in '68 - '69,
In their solo years, they've had some producers alongside themselves in the producer's chair. To name a few, Jeff Lynne (for George and Paul), Russ Titelman (for George), Phil Spector (for John, George), Vini Poncia (for Ringo).
How would we rank them, the good ones and the bad ones.