What are the best options for military service after law school?
If you want to be an attorney in the military, your only real option is JAG.
The other option would be some sort of logistics officer and do defense contracting (the "buy a $600 hammer" guys). You don't need to be an attorney to do that, but a law background wouldn't hurt. You can also get a job with the DOD as a civilian to do this.
You could also decide you want a multi-year vacation from the law and go fly jets or get your grunt on in the infantry. I once knew a Notre Dame law grad who enlisted in military intelligence to get student loan forgiveness. He didn't last long. Pursued a JAG commission once he realized what enlisted life was like.
As far as I know, you can be an Army JAG as either a member of the reserves or national guard.
Navy Reserve, I know they don't bring in civilian attorneys for commissioned duty as reserve JAGs, generally. (No direct commission program for JAG in the Navy.)
Right now, competition for JAG positions is pretty fierce. I wouldn't rank it anywhere near biglaw, but it's probably on par with trying to get a position with the federal government as an attorney.
For example: "The Navy received 923 applications for the 2009 fiscal year, Goldsmith said, and accepted about 75. Slightly more than 8% of the applicants made the cut"http://www.law.com/jsp/nlj/PubArticleNLJ.jsp?id=1202431259048&slreturn=1&hbxlogin=1
As far as I know, there are no signing bonuses for JAG. I think the Marines were the last to offer one, but with civilian sector hiring soft, and patriotism high, the military (all branches) is having no difficulty finding people.
Also, joining either the Air Force or Navy is no guarantee of a short combat tour. When the Army is short of people, they can tap other services for what's called an "Individual Augmentation" tour, meaning you get issued Army uniforms, do Army duty, and deploy for the Army length of time (a year +). The only difference is that your service tape says "US Navy" instead of "US Army".http://www.stripes.com/news/sailors-learn-army-basics-to-prep-for-downrange-deployment-1.47174
One last word of warning during a time of two wars. Chaplains, medics and doctors don't have to engage in combat. (They may be IN combat, but they are not doing the fighting.) In fact, if they do, they jeopardize their status. (This is why the Marines don't have any. All Marines are expeditionary combat resources. So, the Marines get their chaplains and medical personnel from the Navy.)
Everybody else, and that means EVERYBODY is expected to be combat-ready and willing to put a bullet in the forehead of the enemy if the situation calls for it. There are no passengers on convoys. If you're ambushed moving from point A to point B, you are expected to pick up a weapon and start killing the bad guys and breaking their stuff. As an officer, you are REQUIRED, not expected, to assume command in these situations if you are senior.
If the idea of killing somebody or leading other young people to kill and be killed isn't something you want to deal with, then this is not the deal for you.
As for pay, frankly, military pay and benefits are exceptionally good these days. Nowhere near biglaw, but if I had to WAG, I'd say that 60% of lawyers won't do as well as military officers. After you make O-3 (I believe that happens after 2 years for most JAGs), you're basically making $80,000 a year, with continued upward potential. After 20 years, you can retire with a 50% retirement. After 30 years, you can retire with 75%. If you're in for 30, you'll probably be an O-6, at a minimum. So, the pay is substantial, and the retirement is considerable.
You can get an idea of military pay, here:http://www.dfas.mil/militarypay/militarypaytables.html
Keep in mind that in addition to base pay, you also get a housing allowance and meal allowance.
Best of luck.