I know I'm going to break Yankee's heart with this pick (he's already called me a rude name in a PM) but I am going to take the quintesential Americana musical. A musical that beat West Side Story for the Tony for Best Musical in 1957 and a musical where the music, lyrics and story, were all written by the same man, Meredith Willson of Mason City, Iowa.
44.04--The Music Man-Meredith Willson-Play
From Seventy Six Trombones, to Trouble in River City, to The Wells Fargo Wagon or Gary, Indiana, this musical is chock full of great songs. This musical about a con man who comes to a small Iowa town and tries to con them into investing in a boys band only to be undone by the town librarian who he falls in love with is a classic story from a simpler time. Starring Robert Preston and Barbara Cook, the Music Man was a hit from the start, as I said winning 5 Tony awards and beating the Sharks and Jets for the top musical that year. It's songs were covered by many artists, including one "Till There Was You" by the Beatles. Willson's widow later said that they made more money on royalties from the Beatles version of "Till There Was You" than they did on the entire musical play.
The 1962 movie is also a classic and y'all should watch it sometime.