Go to college. Perhaps join ROTC, but go to college. So much changed for me in my viewpoints and thinking ability and capacity from the time I was 19 to now (21, graduating college in May), and I'm thankful for the experience. You'll learn a lot about yourself and a lot about who you want to be. The military will be there when you get out, but you may not have the opportunity to go to college later.
Just my .02, please keep in mind I have not had the honor of serving in our armed forces. Good luck with your decision!