No question Zeppelin. I was having a conversation the other day about the Beatles, Stones, Zeppelin and the Doors, and they made a great point. He said "Anyone could have been the Stones." What he meant, was that the Stones didn't have a serious influence on music in terms of moving it forward. They rocked, no doubt, but they played straight rock and roll, no real innovation, just a great rock show.
I think true greatness in music, or anything for that matter requires innovation, and that was not the Stones thing.