I've always been partial to the 20" AR's. I like the sight radius and the length is more of a blessing than a detractor. I'm not out kicking in meth lab doors with a team so don't need a shorty. I've shot a 16" bbl AR before and didn't like the increased muzzle blast over the longer tube.
Besides, the 223 is sort of a pipsqueak round anyway, and can use all the velocity it can get, ergo longer barrel.
"Always place your clothes and weapons where you can find them in the dark"
"Understand that the enemy is not the enemy in his own eyes ;this may offer you an opportunity to make him your friend. If not, you can kill him without hate, and quickly."