Great question but tough! There are so many crackers but a few stick in my mind for various reasons:
Journey at Hammersmith Odeon. Pre-Glee shudders at Glee Saw them a few times sadly not with Steve Perry, the original (and irreplaceable) singer.
Bon Jovi in '86 - first gig.
Soundgarden pre-first album at, I think, the Marquee (late 80s)
Art Garfunkel - Glastonbury 2016. He started with Bright Eyes and everybody had a tear in their eye. It was hit after hit from then on in. (Best stage is the Acoustic stage)
David Lee Roth - I saw him three times during the Skyscraper tour and he was amazing. Sexist, a bit of a wrong un, but he really knew how to put on a show.
Prodigy at Brixton - not my cup of tea normally but I was dragged along. It was fantastic
Motley Crue at Wembley - how are they still alive? How can they still sound so good?
Finally, Coldplay Sunday headliner at Glastonbury 2016. I rolled my eyes when I saw them on the bill AGAIN, not really a band I get excited about but the party atmosphere that Sunday night (after a tough, muddy, brexit-filled weekend), left us on a total feel-good, light-filled high. Still think they're the audio equivalent of magnolia paint but I can at least appreciate why they are festival favourites now