Focus on the officer career paths available to you after commissioning, and how you might be spending at least 5 years after graduation. Dive deep into that. Reverse engineer it. Once you have an idea of paths that appeal the most, then the Academy decision follows naturally. Think too, about which Service has warfare paths you absolutely want no part of, and you don’t think you’d fit well in, if that’s where you got slotted. The Navy does most of its work on, below or above water. Marines share in a lot of that, except for subs. Deployments may involve months at sea. That’s not for everyone. The Army is land-based, with its own arduous challenges.
Though it may be just a typo in an informal post written on the fly, “marine” is usually written as “Marine” when referring to the United States Marine Corps. That’s just who they are.
The Service Academies and their majors, while important for 4 years, are truly a relatively brief way station to what you are really choosing: years of service as a commissioned officer in one of the armed services. Be clear on that, and everything falls into place.