I don’t think I’m qualified, since I have not seen all such films, and wouldn’t know how to rank them except subjectively., and as JLeslie mentioned, I don’t know if you mean films from musical plays as well as non-musical plays.
Of the ones I have seen, and that come to mind, the best ones in my very subjective gut reaction’s opinion, limited greatly by memory and sleepiness, include:
My Fair Lady
The Sound of Music (1965)
Hairspray (2007)
It sounds like one of the worst may be the recent Cats film, though I’m really sure I don’t know and don’t want to experience the worst musical film.