I've had alot of success buying Military Fares from AA. (They're usually the same price as a regular ticket for me anyways) The chief advantage is that change fees are waived so if your plans change then you'll have a full credit that you can apply to another ticket, no questions asked. Oh, and also, the advance purchase is only something like a day, so that's nice too.

That said, you could also go ahead and buy a standard ticket as you had proposed. My understanding is that you can change or cancel that ticket without penalty so long as you have a copy of your orders in order to demonstrate a conflict caused by the military. I've only ever had to do that once, but it's definitely doable.

Honestly, I'd call the reservations line and get a quote on that military fare before you make your final call. Good luck.