The best will vary depending on price, benefits, flight times, non-stop vs. connection, etc. and what value each individual places on each of those attributes. Look at the benefits of each program and determine which one works the best for you. Being 17 and heading to school, I would try them all and get to know the benefits of each program in the process.

Reading the FF section of each airline's web site, reading the FT forum threads for each airline, and setting up a spread sheet comparing their benefits will help you determine which one works the best for you.

Keep in mind that airlines' frequent flyer programs change, and as they do, the one that fits you now, may not later. AA will undoubtedly go through quite a few changes come next year. Good luck on that 10MM.