So, I was in Marching Band the last two years but have thought about quitting recently, I have potential to become a section leader though during my senior year. I have always ran and really enjoyed it, so I was convinced that it was what I wanted to do this year so I started to run more and get in better shape for cross country, getting shoes and all, but now I’m sort of missing Marching Band. I would never qualify for states or anything but I think that I could try out for winter and spring track, and possibly make it so that I could do Marching in the Fall. I wanted this website’s opinion on this issue.
Just do whichever one you personally prefer. As long as you pick one, colleges aren’t going to care whether it was marching band or cross country unless you are recruited in one of them, and that doesn’t sound likely based on what you said.
bump, with regards to admission offices, which looks best
Hmmmm I’m no expert, but the leadership position in MB might look a tad bit better, however it won’t make much difference.
Although, as a fellow MB kid, you can’t quit band! It’s a way of life! 
jk
I’m with @JeanJacket123 . The leadership in band might look a tiny bit better, but I honestly would just choose whichever one you enjoy more.
Choose whichever activity you would enjoy doing more. Colleges do like commitment and leadership, but they also like diverse interests. Do you have multiple leadership positions for your ECs? This is a tough decision!! Are you definitely sure that you would receive a leadership for marching band? If you aren’t completely sure, then I would go with cross country. It would be better (in my opinion) to choose cross country, especially if a leadership position is not definite for marching band. Would you be willing to do both marching band and cross country? Or would that be too much? If possible, I would try to do both.