As others have stated, #1 which branch can you see yourself serving in? What career path does one have that you want to pursue? If more than one SA meets those criteria, then apply to them.
It is a lot of work. Our DS applied to 4 SA's, all nomination sources, and NROTC plus his top 5 schools. Then you toss in scholarship applications, CFA training, academics, and regular life. It isn't easy.
But the rigors of academics, military training and responsibilities, and physical requirements at any of the SA's won't be easy either. If you really think you cannot find the time to apply to more than one, and master time management, the rigors of a SA may not be for you. And that's okay, it's not for everyone.
But, if you really want it, dig deep. Buy a binder, notate each due date, each deliverable, each point of contact for each SA, and nom source. Use a whiteboard to track all due dates.
And for sure start the process as early as you can. Submit good, quality applications. And good luck!!