It's been a few years since I was a cadet (or in the military for that matter!) But as I recall the local cadre of instructors have a small part to play in your eventual branch (that is, aviation, infantry, signal, etc.)
The input they generally provide on an "order of merit list" or OML. Your standing on the OML goes into your packet that gets sent to a centralized board that looks at 3 things:
Your score at Advanced Camp (used to based on a 1 to 5, now on a 1 to 1000 possible points),
Your GPA,
Your OML (and especially is you are a Distinguished Military Graduate or DMG)
Those things along with the needs of the Army THAT DAY (and they do change day to day) determine 1. your branch, and 2. your component (Regular, Reserve (active), Reserve (reserve))
You can get a GRFD contract-guaranteed reserve forces duty contract. You then are responsible for finding a unit, convincing them to accept you as a 2LT, and then you only spend your officer basic course time on active duty. Of course your packet would not go to the centralized board as you already would know your component and basic branch.
I was in the basic course with several GRFD guys. The Army was flexible about letting them miss a day or two to go interview for full time jobs, and one of them attempted, unsuccessfully, to change over to active duty.
I don't have that much reserve experience, yet I have found it rare for aviators to be straight reservists, and I have never seen a GRFD aviation officer.
Having said all of that, if you are honestly considering the military, when you are ready to pull the trigger (so to speak), here's an idea to make you very competitive on your camp score and OML: Go to basic training as a reservist now. ROTC will tell you that you can go to basic camp and get the same training-it's simply not true. Basic camp is a training environment, but the cadets aren't under any obligation, so a good deal of coddling goes on. Coddling you simply will not receive at advanced camp which is a TESTING environment. At basic training you will learn much more, and faster about the Army, and that will translate directly to a better score and OML. The mission of basic training is to teach warrior skills. These are the same skills that at advanced camp you'll be tested on.
A reserve unit near you needs help, no doubt about it. One thing I would change about they way I did things is to get an aviation MOS, which if you are interested in aviation will put you in a better position to get an aviation slot. Mechanic is better than crew chief, avionics tech might be as good as mechanic.
Just some thoughs...and I got out about 4 years ago so things may have changed. Good luck!
-D