What caliber would you build a 18 inch DMR AR style rifle?

[Mags]

Just curious on opinions here. What caliber would you guys build/buy a 18 inch DMR/SPR rifle?
The 223/5.56 the original DMR.
The 6.8 with the .270 bullet diameter which is normally the minimum diameter for hunting big game in alot of states.
The 308 the best combat caliber of all time (lol).

 

[kanook]

low recoiling and effective for what I need it for. Shot 3 deer and recovered all 3. Closest was 15yds, furthest was 120yds. All down within 30-50yds.