I'm like Silat here, so many good ones, hard to say which was best...
I guess I'll have to say Pink Floyd, Animals tour, 1978 in Houston (Jeppeson Stadium), only better than other times I saw them because it was an outdoor venue. They played Wish You Were Here, Animals, then Dark Side of the Moon as their "encore".
In the rain. Amazing.
Close second, Blue Oyster Cult at the Armadillo World HQ in Austin in 1976, with Bob Seger and the Silver Bullet as the opening act. Their laser show was in full bloom, before any restrictions on power began to be applied, and their musical prowess hadn't yet started a decline. Awesome show.
Some honorable mentions -
Led Zepplin, Denver, 1972. Wow.
Johnny Winter, 1973. Double wow, best guitarist EVAR. (When he'd solo, the crowd was awed into silence.)
Yes, Denver, 1972, but not for their performance, they were stumbling drunk. They just had the good taste to have Edgar Winter and White Trash as their opener, and that was a ROCKING good show!
ZZ Top, Edinburg Texas, 1971. They played in the new university auditorium, and led a little revolt when school officials tried to enforce a "no smoking" rule. The show ended up having the band crowded together in a huddle, playing while about 150 of the crowd surrounded them onstage, passing joints all 'round. It was the first and last rock show in that auditorium

Seompi, Spring Break - South Padre Island, 1970. A local band which featured 3 players - a drummer and two bassists. (Pat Rockhill, one of the bassists, played lead.) It was my first-ever experience with LSD (Orange Sunshine imported by some freaks from University of Kansas, sold in a tent on the beach made from an orange parachute). I could literally see the music as it flowed out of the speakers, it was wonderful

I could go on
culero