As I've mentioned often here, my all-time favorite, actually-seen-on-a-stage musical is A Funny Thing Happened on the Way to the Forum. And if you'd seen the production starring Phil Silvers that I saw in 1970, it might well be your favorite, too. I have since seen quite a few productions of it — some wonderful, some awful — and the awful ones have not diminished my fondness for it.
Something you may not know is when the original production was in outta-town tryouts, it wasn't doing well. Audiences did not warm to the show and its producers were thinking of abandoning it. That was before they brought the great director Jerome Robbins in and he decreed that the problem was that the opening number did not set the show up properly. They tossed it out, Stephen Sondheim wrote "Comedy Tonight" to replace it, Robbins staged it…and the show was a hit.
Robbins directed a lot of hits and in 1989, there was a show made up of excerpts from most of them. It was called Jerome Robbins' Broadway and among its scenes was the opening (only) of Forum. This is a video of it with Jason Alexander in the role that Zero Mostel played in the original. It's a rare chance to see Robbins' actual staging of the number because every director stages it differently with different physical gags. Watching it only makes me wish I could see another good production of it…