Band. 100%. Taking AP Chem vs not taking it WILL NOT be a deciding factor in whether you are admitted. I agree with @twobugs when they say you think youre supposed to take another AP. I actually thought about quitting band for my senior year also so I could take another AP Class. After about 30 minutes of talking to my band director I changed my mind. Band is something I love and it keeps me sane. Its a major part of my life and considering that you have stayed in band for this long it must be a major part of your life too. Its your choice, but I recommend band. APs are great, but do what makes you happy and you will get into the right school for you,