Need to break the drummers down in to categories because "rock" can be broken down into 50+ genres itself. And you can't really compare the drumming of someone like Ringo to the drumming of Joey Jordison. What are we looking for in "greatest" rock drummer? For me it's as much about being original and creative and having your own distinct style of play as it is playing difficult things. I've seen drummers play fast as hell but struggled with slow songs. Ringo isn't one of my favorites, but I respect him because he played his music perfectly and I don't mean that in a technical way, he just played exactly what needed to be played on each song. To me you're great when a song comes on the radio and you know who's playing drums even before you know what band it is. This is what separates the Pearts, Barkers, Carreys, Hawkins and Ringos of the world.