College - high school is very usual on AFF, and in college, you can write about the transaction from teenager to adult :) Your characters can grow more mature, more independent, which can become a lot of interesting stories ^^

College since High school are mostly found like the first commenter said but college is the time where we are a bit more mature than high school and it will be a nice setting to see characters who are either adults or are almost about to be adults

College. There's already so many high school settings. It'd be nice to see a different setting, but that's just my opinion ^^