Call me a traditionalist or an old fogey or whatever, but I love Sousa marches. I can listen to a good band play Sousa marches all day. For the most part, they're so upbeat and a good band can really make them something special.
Saw the U.S. Navy Band recently and when they played "Stars and Stripes Forever," their piccolo players really gave their parts the full ornamentation and made the old warhorse sound brand new.
Marching bands often play popular music. I remember when my sister marched in the high school band in the early 80s, they played "Superstar" from "Jesus Christ Superstar," so pop music was common even then.