Brighton Beach is FAR too overdone for 16 year old boys. I don't think that any of the male Glass Menagerie monologues have high enough stakes to be really compelling to a viewer.
No one wants to see a musical called Thoroughly Modern Mildred.
Hmm, well. It really depends. Maybe you can go to your local perfomring arts place (or somewhere near your town) and find someone who is doing a musical, and get his advice. I've done it before, and it worked out great
some really unusual suggestions:- "It Isn't Rocket Science" from "Stud" (1960's Rock and Roll number, slightly comedic) or "A Brigadier Retired" from "Silver's Ghost" (again comedic but would show off acting talent). The latter is available on i-Tunes either with or without vocals. Follow link through "CDs" to "The World Is My Stage" ... Surrey Dance Music