You should pick the USA because we're practically like 50 countries put into one huehuehue. From California to Utah to Louisiana to New York you will have a very different experience no matter where you go.
Anyway that's nice of your school to pay for it all.
I would be a little wary of Japan though. It always bothers me when I'm watching anime and they call someone from another country (usually the US) a "foreigner". Here in the US if you're from another country we say the country like Mexican or British, not just "foreigner". I don't know, it just rubs me the wrong way.