I'd have said Guns n' Roses were, and if they could have maintained the same quality they would definitely be up there!
GNR < Metallica , GNR = Gayer than Elton John snogging George Michael to a soundtrack of Soft Cell, Communards and Judy Garland.
GnR isn't in the same class as Zeppelin was. All three definitely past their prime. If we're going to list older bands who rise to the level of great then I would humbly submit: Stones Fleetwood Mac (original 1967-1970) Jimi Hendrix Experience Any band with Eric Clapton Beatles