If I could see any music act either living or dead I think it would have to be Beethoven. Without doubt a musical genius, the bigger problem is which piece would you choose to hear? There are so many. I think it would have to be The Emperor piano concerto. Can you image being present at a performance where Beethoven himself is playing this wonderful piece? He was apparently quite deaf by the time he wrote this which makes it all the more remarkable. This didn’t stop him from composing or performing, amazing. The first public performance was given in the Gewandhaus in Leipzig a magnificent looking place still in use today. He wasn’t playing on the night though, that honour went to another gentleman.
I never saw The Beatles or The Stones live but I have a feeling that what you would have heard above the music at a performance by either band would be the screaming. I don’t think that would have been a problem at a Beethoven gig although I am sure there were plenty of ladies vying for his attention at post concert bash. There’s also a very good chance that you would have got a seat, with a view.
Of the more modern artist I think Sinatra would be the one.