Best: A late 80s show at Melody Fair featuring Warren Zevon opening for Eddie Money. Both guys played their asses off and I believe that Money did it three sheets to the wind.
(Honorable mention to the Roger Waters "Wall" tour and any of the handful of Avett Brothers shows I've seen).
Worst: Hands down, Morrissey at the Rapids Theater in Niagara Falls. I took my girlfriend at the time, though I had never heard of any of his music. The lowlight (among many) was when a series of animals being killed in slaughterhouses played behind him for 15 minutes while he screamed, "Meat is murder."