It's in your personal preference. Do you prefer the Army over the Air Force? Or the Navy over Marines? It's which branch appeals to you most. The Marines, however, is a whole different ballgame for females (at least from what I've heard from JROTC Instructors). Check out the websites of each branch, which are provided in my source box. The Coast Guard is now a branch of the DoD (Department of Defense), so if you want to do that check out their website (I did not provide that one). Best of wishes to you in your military career. I also plan on becoming an officer in the U.S. Army after college (hopefully being accepted into USMA, but if not, then ROTC).