What would be the best military job for my fiance?

You need to talk to a recruiter about this. They know what jobs in the military are in the highest demand and therefore the easiest to advance rapidly in... In terms of branches, the Air Force and Navy are fully staffed (so they don't tend to call up forces for combat duty like the Army does, which heavily relies on recruitment and the reserves in times of combat). If I were your fiance I'd choose the Navy if he wants to say out of Iraq/Afghanistan. If he's considering the reserves, the Air National Guard or Air Force would be the best civilian side choice.

yup, if your afraid of him being gone so much, then the military is not the place for him. have him go to college and get his criminal justice degree and then see what he can get for a police job.

If you want to advance in rank, you need to serve combat duty. It doesn't mean that you will be on the front line dodging bullets, but you would be "in country." You don't want to be in a military band. If a war breaks out, band members become machine-gunners and their life expectancy is very short.

What is a band member and how could he avoid that?

Also, what is the likelihood he would be deployed six months every year as I have read

A band member plays a musical instrument in a band. MPs spend a lot of time in combat areas as Military Police. To provide security. If he wants to spend as little possible time in front line combat areas, he should not be an MP. He should find a job in a rear echelon support unit. Like a truck mechanic.

The Navy is way less likely he would see combat, but in the Navy he would have time required at see, unless... My brother did Navy, he specialized in electronics, and had a job working on a hush-hush project. He was guaranteed no sea time. There are certain ways, but you have to be in the know. With other brances, you are more likely to see combat, but with peaceful locations, they can move their families with them. You can't do that when your husband is at sea. I was in the Navy decades ago. Men talked a lot about which jobs kept them from sea or combat, but that was a long time ago. Even if things were the same, I couldn't remember what they said. I do remember lots of the guys transferred from other branches to the Navy because they were "Battle weary", and wanted to stay in for retirement without seeing any more combat. MP is not good if you expect him to stay away from danger. Recruiters will say whatever. I know you want to keep him safe, but even if he were a cop in the town where you live there would be danger. He's a grown man, and needs you to support HIS decision, not jump in on it. If you were married, had two kids, and he lost his job, I could see you helping him choose his direction. Quite honestly, he could finish boot camp, get a tatoo, and tell you he met someone who has more in common with him. It happens a lot.

There is no way anyone here can answer this.

The Navy. We seem stuck on this "land war in Asia" malarkey such that one gets all the benefits of joining the military with appreciably less risk.