Just my 2 cents, but...recently went thru same or sort of, decision.
AR15 - .223, great weapon, ammo cheap (relatively), accurate to 100 yds, lots of accessories, fun to shoot!
M1 - .308, accurate to 300+ yds, expensive to buy, ammo more expensive, fewer accessories
AR10 - .308, Great weapon, plenty of accessories, more expensive to shoot.
My choice, AR15 lower, 6.8mm SPC upper. Terminal ballistics in between .223 and .308. Accurate to 300+ yds. Less recoil than .308. Ammo available locally and on line. Cost between .223 and .308. Seems to be a great compromise. Took two deer this season 180+ lbs, longest shot was 185 yds.