Your question isn't going to be a clean cut answer - we all have different experiences and opinions on "what works" for us, and it may not work for the next guy.
It's all about the weight - how much do you want to carry, and how far?
The .308 sized ARs are generally heavy, and that is a down side for many shooters - there are not many "lite" AR-10s.
The "ethical range" is the same for an 18 inch bolt gun as it is for an 18 inch AR - the bullet velocity is determining the mechanics of the bullet construction on impact, and the target skill is on your end of the rifle.
Without shooting both guns side by side, it's a guess which "one" will be faster, or better.
IMHO - the 16 inch barrels tend to be annoying loud with muzzle flash, adding barrel inches adds comfort - but adds weight.
For me, I'd use an 18 inch barrel, maybe 20 inch in light profile for hunting and target shooting at the range you list.
Which one - I'd build mine on an Aero Precision set, or go with a DPMS if I wanted in at low cost - I can replace anything that may be a problem later.
Caliber - .308, not because its' the "best", because it's easy ammo to get, MSR loaded ammo is getting to be common, there are number of bullet options, and it's one less variable that I need to focus on while learning the platform.
Last edited by AH64guy; 11/26/18.