I'm not sure of the breakdown in the USMC, but I know the Navy has a ton of helicopters.

The Air Force will probably be your highest Pk of setting yourself up for a major, especially if you end up going tanker / transport. Be very wary of the ten year post pilot training commitment, things are a bit ugly now on the Active Duty side with a lot of burned out guys, time away from home and draw-downs* etc... You can get a decent snapshot at Baseops.net Flight Planning, Aviation Weather & Military Discounts (browse the forums a bit). Go Guard if you can.

The flip side is that you will do some very cool stuff flying in the military, and at a relatively young age. No guarantees though, I've met guys who did decent in pilot training and were sent directly to MQ-1's. Do your research here definitely.

I can't talk to the civilian side, but I'm sure there will be a lot of good insight from the guys who have been there, done that.

Good luck to you!