Led Zeppelin easily. I like The Beatles but I don't think they're the end all, be all of anything. As I see them, they were the impetus for everything, but as such, they were jacks of all trades. They did everything well, but they didn't do anything the best, better than everyone else. They lit all the torches but then everyone took those torches and developed them much further before they became the best they can be. Yeah being influential is important, but if that's the mitigating factor we might as well crown the first caveman musician as the greatest artist of all-time.
Zep on the other hand... nobody has ever done that cock-rock, blues-rock thang better than them and you'll have to live about a thousand years before anyone can compete. JMO
