If you think you're going to fly 25k/year or 30 segments, then definitely pick AA. Why? Because if you're a student, you'll buy a lot of your trips in advance. If you make even Gold on AA, you'll qualify for exit row seating on making your reservation, and for free business class seating on the one daily 767 flight to LA and to SF and the one daily 777 to Dallas.

So, it's very likely that you'd never have to upgrade to First Class on American, but never have to have a seat pitch less than 35", with the seat next to you blocked unless the flight is totally full.

And with hubs in STL and DFW, if you want to try and earn your status quicker, you can probably get a couple of nice 6-segment round trips to Houston and qualify for Gold for 2003 using a Gold Challenge.