I'm going to go in another direction here, My vote for the most underrated composer of the 20th century (maybe all time) is Benjamin Britten. He is well respected, but I think sadly under represented in the concert hall and on classical radio. I find his music superbly crafted and of the highest value.
Now watch, Learsfool and others who actually know what they are talking about will burst my bubble and tell me he is a hack.
Now watch, Learsfool and others who actually know what they are talking about will burst my bubble and tell me he is a hack.