Oh my, choosing the best of some 400-500 (and more if we count club dates, summerfest thingies, free shows @ parks during the Sixties and early Seventies, impromptu performances @ my grandparents Sunday "at homes" during the Sixties, etc.) shows over a 50-year timespan, randing from fully-realized Gospel performances by such as Sister Rosetta Tharpe, Mahalia Jackson, Reverend James Cleveland; Blues performances by Howlin' Wolf, Otis Span, Muddy Waters, Hound Dog Taylor (all in the Sixties or very early Seventies era), etc.; Funk acts like Earth Wind & Fire, The O'Jays, etc.; Disco acts (KC & Sunshine, BGs, Gloria Estefan, Gloria Gaynor, Samantha Sang); Punk (The Ramones, Patti Smith, The Jam, The Clash, Sham 69, The Vibrators, The Minutemen, Stiff Little Fingers, The Pogues, etc.); The Who eight or nine times between 1968 and 1976; Black Sabbath 10+ times between 1971 and 1981, then again in the late Nineties w/ Oz and again w/ Dio as "heaven & Hell; AC/DC about 12+ times between 1978 and 1992; Yes about 10 times; Dylan 3-4 times, including Rolling Thunder Revue; Springsteen 9-10 times between 1975 and 1985; Richard Thompson 10-15 times between 1975 and 2005; Metallica 6-7 times, Misfits about half a dozen times, KoRn three times, Slipknot once, Nirvana 3-4 times, Oasis 4 times, Alice In Chains several times... Skynyrd WITH RVZ and Co. mid Seventies, ZZ Top a couple of times in the 70s, Marshall Tucker Band @ least twice... Tangerine Dream, UFO, Kraftwerk, Scorpions, Michael Schenker band... The Grateful Dead ~15 times between 1969 and 1990s... Spirit, Van Halen, Guns & Roses... The Kinks multiple times, The Stones a few times between 1972 and 1975... and even Kiss, early @ their career circa '74 and later fully realized in/around '79. And Bowie. And Television. And Talking Heads. And The New York Dolls. And T.Rex. And The Cure. And the Cocteau Twins. And too many more to recall, much less list here.
Gosh, I don' know if I can answer this question. I was informed only recently that a particular Dead performance that I attended in the Seventies, 1977 to be exact, @ the Hollywood Sportatorium (Hollywood, FL), is regarded amongst Dead cognescenti as one of, if not the, greatest performance ever put on by The Dead. Who knew? All I remember was being sad that Pigpen was no longer @ the band but "grateful" that it was a "good" night for Donna G. Was that, then, the best concert I've attended (but didn;t know it until recently)?
As a geetar enthusiast my vote probably'd go to one of the many Richard Thompson performances, though not sure which to choose, they were all excellent in similar but also different ways. There was my first Black Sabbath, 1971. I was enthralled, but was equally enthralled @ my first concert of The Who in 1968 and maybe moreso in 1972 & 1973. Springsteen '75 was a hot ****in' performance as well, one that ran close to 4 hours. And Howlin' Wolf playin' in my grandparent's parlour for about an hour. Or Curtis Mayfield singing @ that same parlour to my grandmother's organ (Lowrey w/ Leslie 360-deg speaker).
And the last three I'll namecheck: Uncle Tupelo, Vic Chesnutt, and Richard Buckner, each in a very small venue (a bar, in fact, re; UT).
I dunno. Guess I'll vote for Richard Thompson, not sure which to choose, so I'm throwin' a dart and it shall be a show I too in duing the late 1980s or early 1990s, have kinda forgotten exactly when it was performed, but it was in Chicago @ The Vic Theater. It was the first time I'd heard him play, studio or live, "Vincent Black Shadow" (or whatever it's named) and "Beeswing", both performed during "the acoustic set" and both perfect and sublime. And he closed that show @ which he performed three encore sets with an electrifying (and electric) rendition of "When I Get To The Border", a number that RT rarely played (or plays) "in the wild".
* Honourable mention 1: Free (1972 or 1973). My G-d could those two Pauls kick ass, one @ vocals, the other at geetar. A magnificent live sound they had, that band.
* Honourable mention 2: Genesis (1973), Arie Crown Theater, Chicago. Gabriel was ok but it was the magical tones and the note selections of one Steve Hackett that held my full attention.