So many choices - this is a hard question to answer! If I had to pick just one, I would love to have seen Pink Floyd in concert - they were such an incredibly influential band. I think I would choose The Wall concert because it was a culminating work for them, and the integration of technology with the music was reputed to have been very powerful.
I am very envious of #3's list of concerts he attended!!! I am about the same age, but did not have access to the venues in those years.
Since we all seem to be going for big public performances, I will offer a contrarian thought and say that sometimes a very small venue can make for an incredibly moving and memorable experience. One of the best concerts I ever saw was in the early 80s, the evening that the band Orleans just showed up at a local nightclub and played an impromptu set. It was like a private show- dancing a foot away from a band that was in the top 40 at the time, with maybe 40 people in the room, made for a wonderful evening.