A good place to start your research on future industry prospects is on the employment office website. They have excellent information on their stats page and there are 30 of the fastest growing professions. Remember, you only spend what you have invested and the military is no different.
The armed services vocational aptitude battery (ASVAB) can open many doors for you and teach you many marketable skills that you can use when you get out of your military career, be it for four or twenty years. As with all careers though the best way to have a successful career is to plan for it.
Once you've made the best career choice and taken the ASVAB practice test, it's time to see if you qualify for the position. Visit your local recruiter and see what each office has to offer.
Start with the Air Force and then work your way up to the Navy, Army, and then the Marines. The Air Force and Navy are not as powerful as the Army and Marines.
If you go to the Marines first every time they see you going to a different branch to talk to them, they'll tell you trash and they'll get even more insistent all the time. Looks like they bothered you to join you there.
Some people were either very disgusted or let it influence the decision-making process there. It is best to keep confident recruiters through to the end. Once you've found the branch that has the slot you want and the best package everywhere, it's time to take the ASVAB test.