Which academic summer school/camp should I choose?

I think it really depends on what you want to do in college. If you're looking to go into business, or are strongly interested in it, then I would go to one of those programs. If you aren't really sure what you want to do, then the Brown program sounds like a good option. You're right, the Oxford program would be the most exciting and look the best, but you will also have the opportunity to go abroad during college, so I wouldn't make my decision just on that. If I were you, I would focus more on what the program itself has to offer instead of where it is or what will look good. The fact that you are freshman in high school and looking to go to these kinds of programs is impressive in itself. Good luck!