Here's my zero cents (it's the internet,my opinion is not worth two cents
) :
.223/5.56 is an extremely versatile round,and can be loaded with any and all types of bullets. Low recoil in a lightweight weapon make it excellent for CQB situations. Based on my observations of the layout of the town where I live and tales from friends and family who have seen combat in the Middle East,in any type of urban situation you will very likely not be making shots past 200 yards,where the 5.56 round is plenty 'nuff. But that's already been discussed,moving on...
For me,even with a sling on the rifle the .308 is much harder to take faster follow-up shots. The recoil is harder unless you go to a heavier weapon,which to me defeats the purpose of a light-'n-handy battle rifle. I really wouldn't want to run around with a full-size M1A,and the SOCOM 16 puts that big ol' thunderboomer pretty close to the face,I didn't care for it,and I didn't shoot well with it.
Now a good, heavy, accurate .308 seems to me would be great from a fairly secure position where you can take good clear shots,and you know you're good for 100 yards on out. In that instance,bigger is better.
Just my zero cents.