Well, if all you mean 20th century, then there are thousands to choose from. My favorite 20th century is Shostakovich, Stravinsky, Prokofiev, Vaughn William, Barber, Copeland, Faure, Korngold, Sibelius, and Goldmark.
Don't dismiss film composers; it is just snobbery. For example..Rossini became an extremely wealthy man because his operas were perfomed in Casinos. He got a cut of the gambling profits for bringing in the crowds. So while today the opera snobs only perform Rossini at the Met; if Rossini where alive today he would be doing his operas at Caesars Palace in Las Vegas. What we call classical music was in many cases popular music in its day. Beethoven also became a weathy man from his compositions.
All of the old Operas at The Met were the "show tunes" of their day..
Today people like John Williams make millions and are household names the same as Haydn, Beethoven, Rossini and Wagner were in their day. The current crop of "classical" composers need a goverment and/or a university handout because their music is not anything the public will pay money to hear. Pops concerts that play film or other show classical have sellout crowds.
100 years from now they will still be playing John William's music. Most new "classical" gets played once and is forgotten. Most of it will never get played again.
