As others have said; major in what interests you. Obviously, there are a few things to consider.
1. If you want to be a pilot; and you think you'll qualify and not have a problem getting a pilot slot; then what you major in doesn't matter. It can be behavioral science, history, or engineering. It has no bearing on whether you get a pilot slot or not.
2. If you think in the future you'd like to do test pilot; instructor pilot; etc... then a degree in the aero type majors is what you'll need.
3. If you are looking at a different career than pilot; or a good backup in case you don't get pilot; then definitely get a degree major in the type of job you want to get into. I.e. Don't get a degree in computer science if you want to be a civil engineer.
4. Finally; a small number of you will make the military a 20+ year career. Even then, plus those who only stay 5 or so years, you should consider what you want to do with your life after the military. Will a major in a specific area help you? Is that the area of work you eventually want to get into.
Best of luck. mike...