Call_me_jorge said: "I’d like to expand this out to plays performed in the last 100 years. I think To Kill A Mockingbird might outlive the book. And I say that similar to why I say Hamilton will still be culturally relevant in 200 years. It will be continuously taught in the curriculum for our youth."
With all respect - do you really think the Aaron Sorkin adaptation of To Kill a Mockingbird is more significant than ANY other play from this century? More than A Streetcar Named Desire? More than Death of a Salesman? More than A Raisin in the Sun? Long Day's Journey Into Night? Angels in America? Virginia Woolf? I could go on and on and on. I don't even think To Kill a Mockingbird was the most culturally important play the year it premiered, let alone ALL of modern times.
As for musicals, I'm inclined to say something by Rodgers and Hammerstein. If I had my way personally, it would be a Sondheim show, but I think R&H tick more boxes in terms of cultural significance. Sondheim's work may be widely regarded as some of the best work in the cannon, but he was standing on the shoulders of Hammerstein. And R&H had the perfect combination of mainstream cultural relevance, and high-art sophistication - whereas Sondheim has more of the latter, less of the former. R&H's work turned musical theatre into what it is today, and their musicals are still widely loved.
As for which one? I'm not sure. Sound of Music is the most mainstream, but not necessarily the best. The King and I & Carousel are both brilliant, but both have significant issues that make them dated. So does South Pacific, but less so, I think, especially when it's directed tastefully. I'd say South Pacific.