re: Pick one: Elvis or Beatles

Made the most difference? I don't really know what this means. Elvis was really the same type of singer who just sang standards and had a developed and well marketed product in a way like Sinatra or Bennett. He did popularize a new form of music that has been the most dominant in the current era.

The Beatles changed how music developed. Or they were at least part of that movement where it became more so expected for musicians to develop their own music.

I don't really know who "made the most difference." I do know that I prefer the Beatles music.