Personally, I would rather be an anesthesiologist.
For one, its a well know field and I can find the info easily. Neonatology... not so much. No saying there isn't info out there, I'm sure there's plenty. Its just that I can find in 5 seconds on google how many years it takes to be a anesthesiologist, which in fact is 12 years(4 undergrad, 4 med school, 4 residency), not 14. But this is probably irrelevant to you because I'm sure you researched.
Secondly, and probably more importantly, I've seen babies, family members, die in that neonatal ward. I've heard of tons of stories of people with still births, premature infants, etc. Could you take all that? I mean death for people in general, doesn't depress me, but seeing infants, who have never experienced 'life' would kill me. Also, the hours and call schedule. Rough. Anything that involves child birth is gonna kill you in calls: OB/GYN/Neonatal, etc.
Just my 2 cents...
Edit: How are you a high school junior, but you're in the military? That doesn't make any sense.
And on second note, like everyone else said above, find out in med school. You do rounds Junior year and some Senior year. Also, you have electives Senior year, to follow up on added interest. So don't stress about it now.