I'm also a student living in Austin, having occasional trip to Asia (Korea, once a year), and often visiting friends in many places in US. Well, UA is usually the cheapest and the only decent option to Korea, so collecting miles in UA is the best for me. In the end, long-haul matters for collecting miles. Check which airline is good (cheapest) for your frequent destination in China. Also, either UA or CO or US is always one of the cheapest option to any place anytime, it's very easy to get miles wherever I go. Also very easy to redeem as *A has a lot of trans-pacific flights.

AA is awesome in terms of schedule choice, but sometimes it's not the cheapest. Price matters for student.. With 15k asiamiles, I think you can get AA roundtrip less than 600 miles or oneway trip up to 1200 miles. Or get some dining when you visit HKG.