First, it's always been a toss up between the live sides of Back into the Future featuring the Jones / Ryan / Williams / Lewis / Youatt lineup and Live at the Padget Rooms, Penarth which features the classic quartet of Jones / Ace/ Williams / Leonard. The former features a near definitive C'mon (with the Gwalia Male Voice Choir) and the latter the absolutely definitive Many are Called But Few Get Up. I think right now I'd for the latter, especially the newly released double disk edition on Esoteric which includes the entire gig, including a rendering of Spunk Rock that even surpasses that on Greasy Truckers. Both of these are by the Manband by the way (otherwise known as Man; big on the posters lads but damn near impossible to Google!).

Second would be Soft Machine Live at the Paradiso, March 1969.

And third Peter Bellamy's Songs and Rummy Conjurin' Tricks.