First off, what do you want to do in life?

1. If you really want to be a military pilot at all costs, apply to all services, (active, reserve, and guard) which will offer a flight guarantee. This assumes you are OK with helicopters, which will not help your airline prospects much...but they are fun to fly and have great missions in the military if that is your focus.

2. If you want to be a career military officer, stick with active duty, but understand that your track will involve lots of staff work, higher education, politics, and less flying.

3. If you want to be an airline pilot, then I would REALLY do everything you can to get a guard/reserve slot. Start civilian training immediately so that you are not left hanging out to dry if the military doesn't pan out. The ideal situation would be to get hired at a regional airline BEFORE you join the guard/reserves but the timing may not be ideal for that since you don't have any ratings and almost no one is hiring.

If you can't swing guard/reserves, then consider active duty, but be aware that you will want to get into fixed-wing aircraft. You are almost guaranteed FW in the USAF. Navy/USMC is a crapshoot, Army and USCG most likely helos. If do get assigned helos there will probably be opportunities later in your career to acquire military FW time but of course there are no guarantees on that.

As far as enlisting...as a soon-to-be college grad your focus should be on commissioning programs. If you really want to fly, do NOT accept a commissioning program without a flight slot guaranteed (recruiters will lie, don't believe them unless it is in writing). You are correct in that there are limited opportunities for officers to change career tracks, but I have never, ever heard of an enlisted man being denied the opportunity to take a commission (you don't even have to complete your enlisted contract). If you can't get an officer slot, enlisting could help you get a flight slot, but join a guard/reserve squadron which flies an airplane you would like to fly...that will enhance your chances of getting a pilot slot with that unit. Good quality enlisted service will also help when you apply to any commissioning program.

Note that even if you get into the military pipeline there are no guarantees that you be assigned the aircraft you want. In fact the USAF is even diverting new pilots into UAV's...which will do absolutely nothing for your possible airline career.

Also some guard/reserve squadrons are losing their airplanes...if you enlist make sure the squadron is going to be doing the things you want to do for a while (any officer at the unit would know).