Modern English composer.
See also :
Quora Answer : Do you have a favourite contemporary classical composer?
Assuming we're really talking about that kind of academic orchestral composition and not someone working in a more "pop" (including all the underground offshoots of pop music including jazz, rock, electronica etc.) then I guess it's Sir Harrison Birtwistle.
Basically because I used to listen to him a lot when I was a teenager and in my early 20s. (Or at least a lot more than most contemporary composers). I guess it was the fact that he was obviously wildly modern and experimental but you could just about pick out and latch onto fragments of melody and rhythm amongst the chaos, and the theatricality and playfulness made it more accessible and feel less abstract than other composers.
Also, I was very into the early Stravinsky ballets : Firebird, Rights of Spring, Petrushka and it was clear that Birtwistle was following in that tradition.