I first heard Barber's Adagio For Strings in the early 1970s, played by a small regional symphony. This was when it was still an obscure piece of back repertoire, before the revival in interest which has made it into the sort of symphonic warhorse that it has become today.
At any rate, I think I may have stopped breathing a few times during that performance, it was one of those rare moments of pure perfect beauty.
I tend to favor Andre Previn's reading of that piece, I have a recording that he did for a BBC television series that he hosted.