I work as an administrative assistant to the honors program at the college I attend. I’m going to try to say this as nicely as possible… marching band does not differentiate you from other students. I can’t tell you how many application essays the director of the honors program has read about marching band and how it builds their leadership skills. It’s along the same lines as how playing a sport builds your leadership skills. A lot of people do that sort of thing and write about it in their application essay. I would take the AP class. It shows that you can work hard and study hard and are ready for college classes more so than students who didn’t take AP courses. Plus, you’ll still have your previous marching band experience to put on your college application. You can still include that you were in marching band because it shows that you did an activity beyond the classroom and were committed for at least 2 years depending on what you decide to do.