Limiting this to cases where I've seen both the Musical and Film in question:
The Apartment (not saying I don't enjoy PROMISES, but the film is one of my favorites)
Chicago
Elf
Monty Python and the Holy Grail
Shrek I love both the film and stage versions of ONCE too much to compare them to each other.
Words don't deserve that kind of malarkey. They're innocent, neutral, precise, standing for this, describing that, meaning the other, so if you look after them you can build bridges across incomprehension and chaos. But when they get their corners knocked off, they're no good anymore…I don't think writers are sacred, but words are. They deserve respect. If you get the right ones in the right order, you can nudge the world a little.