Saw Simon & Garfunkel at the Albert Hall and the following year in Manchester, and they were very good. This was back in the '60s but my daughter saw Paul Simon more recently in the States, including his farewell tour, and said that he was still excellent. More than she could say for Bob Dylan, unfortunately, who was a sad disappointment. I also saw Leonard Cohen, around 1970, and he was very good too. Paul, Bob and Leonard were always my idols.
But if I had to pick anyone else, I would say Metallica. We saw them at Earls Court and they were superb.