I went through this decision this past year and ultimately chose Army. These are some reasons I did:
(Note: this might not all be 100% accurate, but to the best of my knowledge it is)
-I personally don't want to major in STEM. Army gives very little to no preference to STEM majors when awarding scholarships, Navy and AF definitely care.
-Personally, I don't much like boats or water, and so I don't think I'd like to be in the Navy. I've also heard most AF jobs are more office-type jobs (with the exception of pilots), and, again personally, one of the primary reasons I decided I want to be in the military is to have work experiences different from normal office-type jobs, so I decided AF isn't best for me.
-Army gives out more money. I believe all other branches cap scholarships at $180k, and that's if you receive the maximum amount. My 4-year Army scholarship will cover $200,000 in tuition alone, in addition to over $20,000 in stipends over the 4 years.
-Related to the last point, Army gives out more scholarships and it's generally easier to get a scholarship from the Army than Navy/AF. I don't have any statistics handy to share, but I am fairly sure I've seen comparisons of scholarship winners (GPA, SAT/ACT, Class president, etc.), and if I remember correctly Army is the least picky when giving out money. This isn't because Army officers are inferior to Navy/AF officers or anything like that, but mostly because the Army has a higher demand for officers coming from ROTC.
-More schools (at least of the schools I looked at) have Army ROTC programs. Personally, all 7 schools I was looking at last summer have AROTC programs, and several didn't have Navy and/or AF, so Army worked out better for me.
Again, I'm just a kid and don't know too much about what I'm talking about so don't trust everything I say. I met with ROTC recruiters from every branch to go over their programs and recommend doing that if you can because I think it helped a lot.