I'm a big fan of Copland. His music can be dramatic, sad, joyful, and just plain fun. I also think his music is a good vehicle for personal expression of the performer/conductor. I don't think this is true for all composers–-I cringe at some interpretations of Bach–-but I usually enjoy it when a performance of Appalachian Spring or Bill the Kid contains some individual stamp that indicates the performer is really feeling and enjoying what they are doing. The combination of Copland's timeless compositions and subtle playing effects can be very sophisticated indeed.