I think Stephen Sondheim has written the most beautiful, imaginative, unusual and complex musicals of the 20th/21st Century. From his collaboration on West Side Story, to his comedic songs in A Funny Thing Happened On the Way to the Forum (Everybody Ought to Have a Maid is probably one of the most entertaining numbers ever) to Company and A Little Night Music, which showcase his amazing musical complexity, to Sweeney Todd and Sunday in the Park with George, which prove that if you are talented, ANY subject can be a musical. My favorite has to be Into the Woods, though, which has one of the best roles ever for a woman (several, actually, but the Baker's Wife is amazing).
While there are many others I enjoy, Sondheim is my choice for number one.
The interesting thing is that on the huge musicals forums where I post, both ALW and Schwartz are viewed as "popular" and not particulary "classic." In other words, the way Mozart was viewed in his time
OMG, Stephen Schwartz is SO TOTALLY the best in my opinion!!! Ask anyone who knows me well what my favorite musical is, and they'll probably say Godspell or Wicked. I have yet to see Children of Eden, but I hope I get to see it. I'm gonna go see Wicked this summer. CAN'T WAIT!!