For me it would have to be SWEENEY TODD, no question, with FOLLIES, NIGHT MUSIC and ASSASSINS and INTO THE WOODS following up. I've never really warmed to PASSION, the story just never interested me. SUNDAY IN THE PARK has some glorious music, but it has some of his weakest moments (I absolutely agree about the scene of George and the dogs, easily the lowest point in Sondheim's career).
"If they can get you asking the wrong questions, they don't have to worry about the answers." Thomas Pynchon, GRAVITY'S RAINBOW
"Reality is that which, when you stop believing in it, doesn't go away." Philip K. Dick
My blog: http://www.roscoewrites.blogspot.com/