ya really gotta ask yourself what is the primary function of this AR goin to be? If it is CQB then ya want the lightest shortest AR ya can get, if ya are Varmint huntin, then a HB 20" would be the way to go.
I have a Franken-AR with a Bushy Superlight barrel, it is pencil thin all the way back. it is light and nimble , but it heats up pretty darn quickly , like 30rounds of rapid fire and it can get hot enough for ya not to touch it. As far as accuracy, if i can hit a pie plate at 100yards in happy, im not a competition shooter and dont care if all the holes touch, if i can hit my target im happy.
The superlight barrel is fine, but im not that happy with it, so im having a custom barrel made that will be Fat under the handguards (mid-lenght) and then pencil thin coming out. ill see how that works out. lol