There has already been ALOT of good advice thrown out there. So listen to it all! Make sure you keep copies of everything!!! I mean EVERYTHING. Also see your recruiter with someone who has served in that particular branch before. It helps alot because the recruiter will not throw as much b.s. at you.
I have been in the Army for almost 4 years now as enlisted as a combat medic, currently deployed with a quick responce force infantry group. Being a combat medic I have been the the field with Tankers, Field Artillery, and foot infantry.
My advice to you would be to just join for a short contract first, like 2 years as an enlisted and see what you think. This works very well for the Navy because they tend to have ALOT of educational opportunities for you!
Then you can still go to school and get enlisted experience, if you want to be an officer then become one. You will already have 2 years as enlisted which will make you a MUCH better officer, (from cases that I have always seen). The best officers I have ever seen have always been enlised first.
Also keep in mind what kind of career you want, not all branched will let you pick your mos. So basicaly if you want to be a lifer I would look into Army or Navy, if you want to live a crazy life for awhile, go Marines, if you want to be bored you can be Air Force, sorry had to.
But every branch has there ass kicker groups, Rangers, S.F., airborne units…
So get as much info as you can and sort it out to make your choice. I think the military is a great life, the deployments suck ass if you let em, but there are alot of good things the military can offer, I have done things no civilian could dream of. Good Luck
Dastang