Navy ROTC, info is 15 years old but
You select your specialty about half way thru your senior year. Based upon a lot of factors, but mainly grades, major, and military aptitude. You can major in anything in NROTC and they will still pay, but you get more points towards your selection score for technical and engineering. (I was poli sci)
You select you airframe after your first phase of training. Based on performance and needs of the Navy. (You'll learn to hate this phrase.)
Commitment is 8 years jets 7 years props and helos after wings, about 9-10 yrs total. In the navy you can instruct in the fixed wing trainer after helos so you can still get about 1500 fixed wing time even if you are a helo guy.