It has been a few years since I was a recruiter, but as I recall there was a test you could take, provided by the state, at cost to you (of course), which the Army recognizes as a high school deploma. This is not the GED, but something else. TxMom was also right, 15 credit hours of college also qualifies you as a high school grad. In recruiting your "GT" score means nothing, that is important when you pick your job , called MOS, and while you are in the Army. The score which is important in recruiting is your QT. The QT ranges from 1 to 99, 99 being the best. Recruiters has a practice version which will predict, somewhat, what your actual QT will be. Any score over 50 is considered good, anything over that will only open more jobs to you.
The Reserves are a good bet as is the National Guard, I chose the regular Army and it has worked out well for me. It does not matter which you choose, plan on deploying, the chances are you will. Remember, the Army is a job, there will be days you hate it and there will be days you love it. Another thing to keep in mind, the Army's job is national security, every thing it does is geared towards that, even the room inspections / GI parties; national security does not stop because you want to take a break.
I was a recruiter from 03 to 05, so a lot has changed. If you want the most up to date info call a recruiter. If you have more questions ask, I will answer to the best of my ability.
