I never met a single airline pilot who wishes he could have a worse seniority number .
I'm half joking, but in the OP's situation if he gets an AD pilot slot, he won't be at the airlines for another 14 years if he goes active duty, probably closer to 15-17 depending on how long his break in service is and to finish out his 20. If he continues on the straight civilian route he'll be at a regional in 3-4 years and a major in probably 5-8 with the current retirement situation and projected hiring. That is literally millions and millions of dollars of opportunity cost.
To the OP, I think it all depends on what you want to do. If you want to fly in the military, that will be the longer road at this point to flying in the majors. The flying is way more fun in the military, but there is exponentially more BS associated with it. The camaraderie and friendships are way better in the military. The sense of accomplishment and service are better in the military. The medical benefits are better in the military. The guaranteed retirement is better in the military. The QOL is exponentially better in the airlines (unless you value weekends and holidays off, then the military is a little better until you have some seniority at an airline). The pay is better at airlines (perhaps minus regional pay, but that has increased so much now and upgrades are generally quick now, so it's probably a wash). The flying in the airlines is just a J-O-B...it isn't exactly fun flying. Follow a line and A/P is on 99% of the time. Military flying is way more fun, but can also become a J-O-B.
I think your best bet might be to press with your degree/flying plan, get your CFI/ATP, get a regional job, and along the way rush guard/reserve units. This will be the best compromise to allow you to do what you want (fly in the military) while still allowing yourself to build a longer lasting, higher paying airline career. I've never met a guard or reserve pilot who said they wished they went active duty. I've also never met a guard or reserve pilot who did OTS who wished they'd done ROTC. I wouldn't mess with OTS or ROTC, frankly. If you rush guard/reserve flying units, you are applying for a part time flying gig, in a known airframe at a known location, with some full time orders available for training and possibly a full time gig later on. The gamble there is actually getting hired. They can be competitive...but if you are competitive for an OTS or ROTC pilot slot, you're probably competitive at a guard/res unit.