My DS graduated/commissioned as Army 2Lt. in May '15. This was his circuitous academic path:
He entered college with a declared major of Chemical Engineering. He entered with a full complement of AP classes and three semesters of college calc, so he had more wriggle room than most other engineering students.
Sometime in his sophomore year he decided that he hated engineering, but still loved Chemistry and Math. He also discovered that neither the Chemist nor the Engineer would go be pushing any limits without a solid computing background. Even if he loved engineering, his schedule and MS classes allowed no room for any electives.
He changed his major to Chemistry. This freed up his schedule to add computer science classes, Arabic, work in a Chemistry lab, and keep up with AROTC.
WARNING: Do not assume that you will be allowed to change majors. Some switches are easier than others, but DS sweated it until he got the okay.
He is currently in Signal BOLC but possibly aspires to transfer to the Cyber Branch which last year only took CS and CE majors. His BOLC classes are heavily geared towards communications which includes a heavy dose of CS. His class includes everyone from MIT STEM grad (not him) to History major from Big State U with zero CS.
Bottomline, he has ended up almost exactly where he wants to be--Active Duty, Signal Corps, off to his first duty station (in the Middle East) next month--but nowhere close to where he thought he'd be 4 1/2 years ago when he showed up for PT. Furthermore, he is not where he is because of anything he had much control of. Whether it was switching his major, getting AD and his first choice branch and Duty Station, there is randomness to the outcomes you should be prepared to accept.
OP should pick what you love, be realistic about time management and treat ROTC as seriously as you treat anything you're doing. As far as what to put down for your major, simply pick one of the STEM majors. The Army will favor STEM over non-STEM, but you better have the real academic chops to handle the workload. If you end up with enough credits to double major, then great. But, don't kill yourself in the process.