Have never seen a production of The Music Man (I happened to visit New York when the Hugh Jackman/Sutton Foster production was playing, but the prices!!!), but it has some great songs, doesn't it? "Rock Island", "Ya Got Trouble", "Good Night My Someone", "Seventy Six Trombones", "Till There Was You", and more.
My favourite show is Les Miz - has been ever since I first heard it years ago. Vying for second place, depending on my mood, are Ragtime and Falsettos.
Favourite new musical is Kimberly Akimbo - I haven't been so charmed and moved by a show since I saw Fun Home. I don't know though how much of my reaction was due to the cast (led by Victoria Clark, who was beyond transcendent) and how much of it was the show itself. A lot probably - David Lindsay-Abaire's book and lyrics were sharp, and Jeanine Tesori is arguably the best musical theatre composer working today. Will have to see a few different productions of it (and really hoping to get the chance) to know for sure.