I don't see any thing wrong with joining the military with the intent of getting a leg up on an airline career. We all have our own varied reasons for joining, and most of them are legit (I had no interest in airlines at the time).

However...you need to go in with the enthusiasim and willingness to do the military service to the best of your ability. Otherwise you are doing a disservice to us all (and yourself).

With that said, I would suggest ANG, USAFR, or maybe regular Air Force if you are interested in airlines. The Navy/USMC have a lot of helos, and you have a high likelyhood of getting assigned to fly them. There is no recourse or appeal, and by then it's too late to back out.

Helos are fun to fly, but helo time will do almost nothing for your airline career...the time just doesn't count at most airlines. The fact that you were an officer and aviator will give you a leg up with a major, but you will still have to get your fixed-wing turbine time before you can apply. You may be able to do this as a military instructor pilot, but odds are good that you'll need to build time at a regional after you finish your military obligation.

With the ANG/USAFR, you know what type of airplane you will fly before you commit. With active USAF, you have a much higher chance of getting a fized-wing aircraft.