Ringo without a shadow of a doubt.
Obviously it’s not John or Paul. People that say George are missing the point. In the 7 years the Beatles were recording, George wrote 3 undisputed masterpieces in this entire time – Here comes the sun, Something and guitar gently weeps. John and Paul often wrote 3 masterpieces or more each sometimes just on one album, yet there are people out there that are deluded enough to believe that George is on the same level. If anything George is overappreciated. Thanks to John and Paul he was able to take his time and develop his songwriting at his own pace…
Ringo on the other hand, people say stupid things like he won the lottery. Ringo is one of the greatest drummers in rock and roll history. He could play it simple and he could play it complicated and always did what was best for the song. Plus he doesn’t get enough credit for the other things he brought to the table i.e. his appeal to the kiddy market, his acting talents and above all, his ability to be a calming influence in a band full of egos.