I voted for Zep II. While Rock & Roll may be one of my favorite Zep Tunes (right behind Communication Breakdown & the Ocean) I never cared for "Battle of the Evermore", "Four Sticks", & "When the Levee Breaks" so it brings IV down for me. I love the whole flow of Zeppelin II (except for the drum solo in Moby Dick(I always thought Moby Dick was a Venereal disease!) but the rest of the song kicks ass)