Cliched answer, but probably the Rolling Stones. Saw them at Wembley in 1999, cost maybe 45 a ticket. Best value EVER. It would cost an arm and a leg to watch them now, but you'd still get your money's worth...

Very tough one, my first was Stiff Little Fingers at Bath Pavilion in 1980, I was 13 or 14 so always sticks in my memory. I saw Elvis Costello headline Glastonbury in 1987, he played solo for an hour then did another hour with the Attractions, absolutely fantastic, he played all of the hits. R.E.M. at Birmingham NEC on the Green world Tour 1989, the gig was sold out but some how me and the wife (now ex) managed to get cancellation tickets right down the front. it was one of those gigs that you just didn't want to end and to see 10,000 people going mental when they played 'It's the end of the world as we know it' is a memory I'll never forget. And finally Pulp at Cardiff University in 1985. The tour had been booked before the legendary Glastonbury show and before 'Common People' had become the anthem of a generation, so it was at a small venue, they opened with 'sorted for E's and Whizz and it just escalated from there, pure bliss, the best gig ever.

jackie lyntons happy days band with graham cooper (cupcake) on guitar at the golden lion in fullham for the live recording of the album till were blue in the face . most musos say savoy brown was jackies best work but not in a million years. if i had to pick the two best live albums ever recorded i would pick we want billy (billy fury) and till were blue in the face, in that order. although if i ever get to see tuba skinny live my choice may change.

Eagles
Living Colour
Clutch
Senser
Corrosion Of Conformity
Metallica
(Early) Machine Head
Sepultura
Motorhead
Aerosmith
Warbringer
Reel Big Fish.

Different era to most of these posts, but...

Buddy Rich big band

Dave Brubeck Quartet (Joe Morello, is the Governor)

Woody Herman

Chris Barber Band (played with nearly all of its members, but sadly never the band).

Oh, and the LSO: wow.

Best live band human league 1981 rainbow when electro music really took off

Definatley Why Don't We they are so awesome!

Elizabeth I think you refer the human league being awesome , in which case yes they were just setting out in 81 , I loved their early lps the ones with original human league mostly, they were very atmospheric I didn't see the early stuff live I'd been too young then.
It's the same with Toyah Wilcox was totally unworldly and I'd love to reproduce the early toyah act on stage - even Toyah herself won't do this probably because the energy is such that she can't - , I'll have to think about why she can't do her old stuff the way she used to do it , maybe the style just don't suit her now at her ge , but I think it's more to do with where she's at in life , she's just not in that state of mind .
Are you interested in electro too ?

Muse for me closely followed by The Darkness

For me it'd be a toss up between Skin (neville MacDonald and Myke Gray, not the other skin), or Airborne. Both rocked the 02 Academy.

Nightwish.....Wembley Arena Dec 2015.....by a country mile (and I've seen a lot).

Ram Jam club in Brixton late '66. Saw John Mayall with Eric, then about three weeks later went back there to see....Cream!
Yes I really am that old.

Oasis @ Knebworth. 10th Aug 1996.

Closely followed by Prodigy at Nynex (M.E.N Arena). Same year I think.

The Clash live always took some beating! The Clash at Lewisham Odeon February 1980 was certainly an epiphany for me.