Really showing my age here.
Best show I ever saw was August Jam in Charlotte, NC in 1974. I was 19 years old. The show started at 10am on a Sat morning and went into the wee hours Sun Morning. Allman Brothers, Emerson, Lake and Palmer, Black Oak Arkansas, Foghat, Ozark Mtn Daredevils, Marshall Tucker Band, PFM were the prominent acts.
Drove there from Orlando, FL with three buddies and got right in the middle of the infield. Set up a tent and had an amazing view of the stage. I saw things that I had never seen before, like girls running around topless.
ELP left a lasting impression on me. Their stage tricks were unmatched by anyone else, and there was a fireworks show at the end that would put anyone else's to shame.