The recoil on the .223 is not nearly that of a 30-06 so it would be alot easier to keep your rifle on target. .223 can be carried in larger quantities and fired faster so it is ideal for automatic weapons.
I have heard that in a few cases .223 can actually knock people down; not by force, but because of the shock of the wound, even if they dont get hit in the torso.
I would choose the .223 for combat.