Hmmm - that's a tough question: Frank Zappa and the Mothers of Invention were great; Genesis (the original group) on their first three tours, the San Francisco Orchestra (with Zuben Mehta conducting) the Tchaikovsky First Piano Concerto; Emerson, Lake & Palmer, (for that matter Greg Lake, Asia, etc.); ACDC's first Thunderstruck tour; Deep Purple; Blue Oyster Cult; Humble Pie; Gentle Giant. My favorite concert, although it may not have been the best I've seen, was Procol Harum at Covent Gardens. Gary Brooker and Robin Trower were still friends and the music was more than I could have expected even from such virtuosos.