If you had access to a time machine, what concerts would you go back to see?

@laxiotakis, I agree that if I could only pick one music festival to go back in time to see, it would have to be the Monterrey Pop Festival. But, the Atlanta Pop Festival (aka Byron Pop Festival) would be a close second. Either way, you would have seen Jimi Hendrix. I have multiple friends who lived in Georgia at that time who could not go because they were too young to drive, and their parents wouldn't let them go.

@Ihasaguy, I caught the Beck - Bogart & Appice tour in 1973. That one was special. 

Early Zeppelin
Early SrV
Mid Stones
Late Hendrix
Anytime The Smiths

@cheeg, that is a great story! I saw Santana and Clapton together in the summer of 1977. They took turns being the opening act and the headliner, so they were very competitive. The show ended with both bands on stage together for a 20+ minute jam session. To this day, I've never seen anything comparable.

But, my most memorable concert story involves Clapton's 461 Ocean Blvd tour in 1974. The show started normally enough with an acoustic set by Clapton and his backing band. After that ended, Pete Townsend walked out and played an unaccompanied version of "Pinball Wizard" on electric guitar. Everyone was looking around wondering if they were tripping or if somebody had spiked their drink. Pete did not return until the final encore ("Layla"). Clapton reappears with his band and starts his electric set. I'm sitting in the upper level near the back row as far as you can get from the stage. Halfway thru the 2nd song, I complain to my friend that I "can't hear the drummer." The guy sitting in front of me laughs and hands me a pair of binoculars. The first thing I see is two of Clapton's roadies hoisting Keith Moon back onto the drum stool. I watched him play for 30 seconds and then fall off again. Now I start laughing and my friend is looking perplexed. I hand him the binoculars and say "this will explain everything!"

9-74 - Roosevelt Raceway in Long Island - Crosby Stills & Nash, The Beach Boys, Joni Mitchell and Jesse Colin Young 

11-75 - Stephen Stills - solo acoustic concert in Boston