Having been there for both, it has to be Elvis. Elvis was like nothing most of us had ever seen. That's not to take anything away from the Beatles, but if it wasn't for Elvis, there wouldn't have been mainstream rock and roll. Even though Ed Sullivan wouldn't televise him below the waist, we all knew it was cool. The Bealtes did not write their early hits, they were covers of Bo Diddley. Chuck Berry, etc.
The Beatles became a huge influence. They wrote most of their songs, something most artists didn't do. They wrote songs of love and peace in a time many of us were questioning the values of Eisenhower America (and I know LBJ was President when they hit the States). But those songs came later.