I'm not being a d*ck, so please don't take this the wrong way, but if you're concern is avoiding combat, the military (or at least the Army or USMC) is probably the wrong place for you.
I say this having had 9 years on Active Duty, which I entered thinking that I would do my best to avoid combat.
The problem with having this mentality is twofold:
-Combat might find you even when you're not looking for it; this happened to me. By avoiding combat you risk not having the proper mindset to ensure that you and the people you work with survive it when the unfortunate happens. Yes, being a JAG attorney does not typically involve firefights. But there are JAG officers on bases that often get attacked by mortars, rockets, car bombs and suicide bombers. And JAG officers do leave the wire, during which time they might be in charge of a column of vehicles moving through hostile area. Furthermore as a commissioned officer, in the event that you and your unit are captured, you're likely to be the highest-ranking, and therefore in charge of attempts to survive, evade, resist and escape. Bottom line is that, when you're in the profession of arms, you don't want to avoid thinking about combat. A big problem in service units has historically been that they avoid doing combat training (marksmanship, basic maneuvers, first aid, land navigation) because their officers assume that they will not see combat; consequently, when they are confronted with danger, they suffer abnormally high casualties.
-Having the mentality (as I did) that you want to avoid combat means that you are likely to be a cultural misfit in the Army or USMC, where a gung-ho mentality is valued.
Like I said, I'm not talking down to you; I'm just talking from my own experience as a guy who entered the Army wanting to avoid war, then having a rude awakening when he couldn't.
As far as Army vs. Navy, etc. I'd say the two hardest things about being in the Army is that there are few enjoyable places to be stationed, whereas the Navy and USMC are typically close to the beach, and the Air Force is more often near bigger cities than the other services.