Broadway/Off-Broadway/regional/foreign.
My own experiences:
Play:
Best: The Roads to Home, Dry Powder.
Worst: A Life, followed by Dead Poets Society, Aubergine, The Encounter, Incognito, The Present, The Babylon Line, and that travesty of The Cherry Orchard.
Musical:
Best: Alton Brown: Eat Your Science.
Worst: Off-Center Jamboree. It had to be seen not to be believed.