Another tough question! But being a movie junkie, here goes…
I have to say that the Fred and Ginger musicals are the most enjoyable to me, maybe because a lot of the music in them is classic–Gershwin, Cole Porter, Irving Berlin. Of course, almost anything with Fred is worth watching. Also in 1936 is the gem “Showboat” (on TCM the other night) with Irene Dunne and Allan Jones and Paul Robeson, who sang the definitive version of “Ol Man River”. Ms. Dunne had a lovely, operatic voice that she used a lot prior to her making those wacky romantic comedies later in her career.
From the '40’s, I like “Yankee Doodle Dandy” and “Holiday Inn”, which first introduced the song “White Christmas”. Then you have all the musicals with Judy Garland, like “Easter Parade”, “The Harvey Girls” and “Meet Me in St. Louis”, which introduced that other great Christmas song “Have Yourself a Merry Little Christmas”. Also Gene Kelly in “On the Town” and “Anchors Away”.
There were the great Rodgers and Hammerstein musicals (“Oklahoma” “Carousel” “The King and I” and “South Pacific”). Of these, I think I like the music of SP the most. Then there was that wonderful version of “Kiss Me Kate” in '53 with Howard Keel and Katherine Grayson. And Ann Miller–wow!–gave her very best performance ever. Kelly made “An American in Paris” in '51, but a really underrated musical from this time was “The Band Wagon” with Astaire, Cyd Charisse and Nanette Fabray. (Oscar Levant–gotta luv him!–was in both) For trivia buffs, also starring in “Bandwagon” was actor/dancer James Mitchell, who later went on to play Palmer Courtlandt in TV’s long-running soap opera “All My Children”. Another fav musical of mine from the 1950’s was Judy Garland and James Mason’s “A Star is Born”. How could you not love lyrics like “I was born in a trunk in the Princess Theatre in Pocatella, Idaho”?
I like “West Side Story” and “The Music Man” and “Funny Girl” (one of my favorites too!) from the '60’s; “Cabaret” and “Jesus Christ Superstar” from the '70’s; and “Evita” from 1996. Antonio Banderas was actually pretty good as Che, although I wish that Mandy Patinkin had played him in the movie instead. I don’t really care for more recent stuff, except maybe for “Les Mis”.
Other “musicals” that I liked were “Springtime for Hitler” from the movie “The Producers”–the version with Zero Mostel, please, not that other thing; and “De-Lovely” which was not so much a musical as it was a movie about a guy (Cole Porter) who wrote musicals.
Did I miss anything?