I have no idea whether this applies to the American military, but you may want to ask about the differences in pay among the trades. Up here, tech trades often come with higher pay, plus longer periods of paid training, and sometimes a promotion once said training is complete. Trades like communication techs, weapons techs, electrical/mechanical engineering, that kind of thing.
I had no time for any of that myself; I signed up to kill the enemy. But if you're a more forward-thinking man than I, you might consider those others.
Here, pay is strictly based upon the rank structure. However, some high-demand jobs offer enlistment incentive bonuses, awarded to troops once they complete their training. This means basic + tech schooling, includes a bunch of conditions you have to sign off on, saying you understand all the ways you could possibly NOT be awarded said bonus, and tends to require the troop to be proactive in making sure he/she gets the bonus once he/she HAS completed all required conditions. Oh, and it's taxed at about 28%. In the Marine Corps, the brokest branch of the four, where Marines are always encouraged to do more with less, I had a $4000 enlistment bonus that was reduced to $2880 after taxes, and I had to wait about 4 months after I was in the fleet before I saw it. Other branches tend to offer more generous enlistment bonuses.
As far as the original poster, this is going to be your life, so make sure you're thinking long and hard (*snicker*) about this. It's not gonna be just a job that you can quit if you don't like it. It's a commitment to serve, for a period of several years, whether you like it or hate it. As far as what branch to go into, any branch is a good choice, but it depends upon what you want out of the military. When I was still in high school, about 11 years ago, I thought about joining the Navy, since my father was in the Navy, and I thought I might try the same thing, with no other logical basis to my decision. In high school, I wore tie-dyed shirts and had hair almost down to my ass. At the school job fair, the Navy recruiter looked me up and down with a dirty look, handed me a business card, and said "Call me if you're interested." After that, I was not. I headed over to the Army booth seeking information. The Army recruiters seemed more interested in talking to other students about football than career options, and ignored me. I'd have checked the Air Force booth, but he was a no-show. I reluctantly approached the Marine recruiter's booth, as I felt it was something beyond my capabilities, but the recruiter took an active interest in me. He initiated the conversation, didn't judge my appearance, and in general, was very personable. The next year, when I was approaching graduation, the recruiter followed up with me, and kept my interest. I kinda jumped on the train on impulse, but I didn't regret it. I didn't really know what else I wanted to do, and all the college brochures started to look the same to me, and gave no useful information. I enjoyed my eight years with the Marine Corps and took a lot of my experiences with me to the civilian world. Wow! Big tangent! Anyway, think about what you want out of the military--the experience? The benefits? What piques your interest?
It's also probably gonna be difficult trying to decide what type of job to go into, since you don't really know any firsthand knowledge of what each job entails, but as previously stated, do your best with the ASVAB, as a high score will provide you with a larger number of choices. If you can, I recommend picking a job that will teach skills that are marketable in the civilian world. If your job ends up being too military-specific, you can always go to college while you're on active duty.
It's a big decision to make. I know I had more to say, but I'm tired and I can't think straight. Good luck with whatever you decide! If you have any questions, you're more than welcome to shoot me a PM. Good luck with whatever you decide!