Best- Dave Brubeck last June. His drummer, at about age 70ish, could play as well, if not better than, Mike Portnoy. He got up on the stage with nothing but the instruments and microphones, compacted in the middle of a huge stage (Eastman Theater), and proceeded to give the best show I've ever seen. I don't care how much pyro you put on a stage, how much production you throw into that, no show (of any form) will ever top what came out of those four guys that night.
Worst- One year I got dragged to a Christian-rock festival. Some of the bands were good, but on the other hand, some weren't so good.