I figure it is all about trade offs.
.223 has some advantages, you can carry more ammo: That may be great for the military, but I'm just Joe-Schmoe shooter. If I get into an engagement that requires 300+ rounds I'm probably dead anyway. Plus I always get a kick out of the Gun Shop commandos (hats off to KSFreeman for his quote "Freedom's Last Hope)
who are going to head for the hills, and they can carry an extra 100 rounds of ammo. Good for them, except most of the ones I know get winded going up the stairs. So moot point for me. If you are in good shape, and have the correct gear, then you can comfortably carry 300 rounds of .223 or 200 rounds of .308. I've done 300 rounds of .308 on a hike once, (PvtPyle's death march/web gear test), and it does get really heavy.
.223 recoils less: I'm a big dude, and very recoil tolerant. I don't think either one kicks much at all. I can do several hundred rounds through my FAL in one day and be fine. But if you are sensative that way, perhaps the .223 is the way to go.
.223 is more controllable in full auto: Moot point for all of us non-military, non-sworn, types. It is dang hard to legally and $-wise to own a select fire weapon, so controllability on full auto is about as usefull as mudflaps on a camaro.
.223 weapons are shorter and lighter: Anybody ever play with a DSA lightweight FAL carbine? Very slick. But I will admit, the average .223 weapon is much handier.
I will say that the AR series in .223 is quicker on follow up shots than a comparable .308. If you look at the top 3 gunners, there are only a handfull of shooters who can hang in there at the top shooting a .308. Just because of the split times on targets that require multiple shots.
.308 goes farther, hits harder, and works better in the wind.
Personally, I think they both have their uses.
And for a 3rd option, if you are very poor, get a 7.62x39 because it is only $80 a case!