This is a no brainer for me, especially as we've had this before.
The very best I've ever seen, for varying reasons -
Little Feat at the Rainbow, 1975 (I think I described this in detail in the Feat topic.)
Bruce at the Hammersmith Odeon, Nov. 1975, (his first concert in Europe, legendary)
Bob Marley at the Rainbow, 1977 (yes, I really was there!! - another legendary show)
Grateful Dead at the Bickershaw "festival", 1972 (two days freezing in the mud worth every minute)
Kind of stuck in a time warp, huh?
I've seen many other fantastic shows, like every single time I've seen Bonnie, but these are the true killers for me.
Far and away the most memorable experience I've had since the 80's was my utterly gobsmacking introduction to Joe last July, a moment that literally changed my life.
RIP Iron Man
Rock On and keep the Faith