Should I pursue becoming a USAF Officer (ALO) or a USMC Officer?

Reading you question narrative, it sounds to me like you want an opportunity to lead service members in the ground warfare environment. If that's the case, then my advice is to look seriously at the Army and Marine Corps. The Air Force and Navy have very few officer billets in which ground warfare is a primary mission.

Air Liaison Officers are most often rated officers (pilots, navigators, systems operators) who can bring air combat or air mobility expertise to their assigned ground forces units. To get there you would have to be commissioned, complete training as a pilot or other officer aircrew position, gain experience in an aircraft that either supports ground forces or provides air mobility. Then complete an air-ground operations course to familiarize you with the way the ground forces and air forces work together. This is a 5 to 8 year path.

The Army and Marines offer opportunities to lead troops in ground operations after a few months of OTS and officer advanced individual training. Time from commissioning to leadership opportunity, usually as a platoon leader, is less than a year.

It's also important to understand the Services assign different levels of importance to missions and positions in various MOS or AFSCs. (Major over-simplification follows.) The missions of the Army and Marine Corps are to fight and win the nation's wars on the ground. The Marines get there from the sea and air. The Army gets there from the ground, sea, and air. Consequently, officers in the combat arms of the Army and Marines (infantry, armor, artillery, etc.) often have higher promotion rates. The Navy is all about sea power. They operate surface and subsurface ships to control the ocean environment and launch strikes against sea and land targets. They have their own air force (Naval aviation) and their own army (the Marines). The Air Force mission is to fly, fight, and win. The key leadership positions normally go to pilots and other aircrew members who command and operate manned and unmanned air and space platforms. Non-flying officers can do well in the Air Force and often handle great responsibilities, but never serve in command of operational units taking the fight to the enemy.

I strongly recommend you talk with an officer recruiter from all 5 armed services. Spend some time researching the missions and functions of each service. Select the Service that is the closest match to what you think you want to do with your life. Also, understand which Service will give you the best deal in terms of accession date, potential credit for advanced education, and guarantees post-commissioning training or school.

As far as family life goes. The further from the front line your job, the more likely you are to be "home for dinner" every night. The front line officers in all services are subject to short-notice and extended deployments away from their families. This is often difficult for the spouse and more so when children are involved. The Air Force usually has the best on-base living quarters, recreational facilities, and shopping.

(Join to see) You are soon to be married, and children are always a possibility. What does your fiancée think about your joining the military? Have you had discussions with her about the amount of time that you would not be with her while in training, deployments, etc.?

What is your degree in?

You're in the same boat as I was. I decided to go the USMC route and join my local Officer Selection Office. For me it was about the physicality of the Marines, the Air Force PT Standards were a joke to me and I just mesh better with the prior service Marines I've met so far. ALO is a cool AFSC, but very competitive. Currently I believe the Air Force has all their slots for OTS 2019. I'm looking forward to working towards Selection for OCS at Quantico and TBS after.

TACP works on Army Posts. You don’t have to live there as an Officer. You’ll ya e to assess and pass AAA for 13L ALO before they will guarantee you a slot. There should be a USAF Special Warfare recruiter in your area. Ask a regular recruiter. I can’t tell you jack about USMC
XOXO
TACP dude.

https://www.navy.com/careers/research-physiology

Here's another...you wanna go this direction, (A), it'd make a good deal of sense, and (B), you'd have a pretty decent chance of going masters level of Ph.D., so trust me please, and look at these really seriously, OK?

https://www.airforce.com/careers/detail/aerospace-operational-physiologist

This, I assure you, would quite possibly offer you all the intellectual stimulus you could possibly ask for while on active, as well as be precisely what you'd trained to do in the first place, the last one is good, this one, however, I honestly think is closer to suiting your ambitions....

https://search.aol.com/aol/search?q=%22exercise%20physiologist%22%20usaf%20or%20usn%20or%20army%20or%20usphs&s_it=loki-tb-sb

Look through these first, I'll try to narrow them down more specifically, to try give you a decent idea of whether you'd meet the minimum needed background...also, what's your GPA, what were your grades, as I'd mentioned, and what specific serious science/math (STEM) coursework have you actually taken thus far, so far as you can elaborate, knowing would help me try to help you a good deal, honest, as I'd said, OK?

I saw you'd mentioned your major here, which I did find interesting, certainly...have you wanted to go for masters and/or Ph.D. in it, or grad-level coursework in any other field? Also, purely out of curiosity, being as you're exercise physiology, would you even think about trying to go for something in any of the services that would be clinically related? I only ask that, as, if you might possibly at least be willing to entertain the idea, I think I could suggest various possibilities to you; I gather, as you'd said, that you'd wanted combat, I get that, however, I'd ask you to please think about what I'm going to say here, relative to the other question you asked. When I went in, as I'd explained to you, I'd gone with totally the wrong recruiter; where that becomes germane to your other question was that I was given a field guarantee, as well as option of five places to pick from to be assigned on a first tour. What I didn't realize, unfortunately, was that I'd have exactly maybe 4-5 days to make up my mind about where I'd wanted to go, aside from totally going into the wrong field, for, as I'd explained, the simple reason that I didn't know what questions to ask, who to ask them of, or have the time, or had taken the time, to have looked into the whole thing properly. Now, given that you're exercise physiology, that military clinical group I'd sent you a link for, AMSUS, could be a very, very good thing for you to look at. Yes, I know it's not combat; yes, I gather your heart is set on it, I obviously fathom both of those points. Here's the thing, however, as I'd also explained, you can plan this, and plan this, till quite literally the cows come home, and, sooner or later, no matter how carefully you plan what you'd seek to do, eventually, inevitably, reality is gonna intrude, and you're gonna wind up needing to make lemonade out of your lemons. I don't say that to be a cynic, I say it to be a realist, and for the simple reason that, if you're exercise physiology, you're immeasurably better off building from what you were expressly trained to do, not because of other ambitions. I had multiple conflicting ambitions, way too many, which considerably contributed to my totally bollixing up where I'd wound up, who I was under, what I was doing, and the God-only-knows unbelievable disaster that ensued for me. So, humor me for a minute, and, for the moment, try, however hard it might be, to curb your ambitions, and let me suggest things for you that are directly related to what you've expressly been trained to do. I'd be quite certain you could eventually serve overseas somehow as an exercise physiologist, possibly in a hospital and/or other clinical facility in an allied country, possibly in a combat zone, if such possibilities exist at all you might request, or in a CONUS (continental U.S.) facility someplace. I tried, while I was in, to actually look at seeking to go interservice to go naval flight officer (NFO), I actually was med examined for it, and passed; what I didn't reckon on was that I was having a total adventure fantasy, seeking to escape from pure office-based engineering work for something exciting, which, while the analogy might not perhaps be exactly precise, could well be said for your ambitions here. Then, too, you've got the whole aspect of wanting to get married, and, while I fathom you and your fiancee have discussed the whole active-duty thing ad nauseum, certainly, I'd point out that she might well be considerably happier knowing you'd be doing work directly related to your degree, even if that isn't necessarily giving you all the emotional charge and excitement you'd certainly be seeking in combat. I've been around a LOT of bureaucratic blocks, more than I even like to recall most days, and I can tell you a good many day-to-day realities, as I'd said, that, even if not as exciting as being an ALO, certainly, would at least giver you a modicum of family stability, as well as be directly related to what you apparently went to school for in the first place, you know? I only mention all that as further food for thought, honest; lemme send you stuff more suited to what your bachelors is actually in; it'd also help to know precisely what type of work you do, if it in fact directly relates to exercise physiology at all, or if you went and did something totally different, instead, OK?

And I'd seen you'd said you're bachelors already...it's obviously help to know if you also had associates along the way, as well as your grades, GPA, and specific STEM and/or non-STEM actual course titles, so far as you might care to elaborate at all....