I'm fond of the 12.5" barrels. Noticeably less abusive than the 10.3 or 10.5 but retains the handiness.
I've got a 10.5" barrel on one of mine. It is still long enough to use a carbine gas system as opposed to a pistol length gas system. That coupled with a KX3 type muzzle device should keep your rifle running flawlessly, assuming you do your part.
+1 on the 12.5" barrel mine is a kino configuration.
I'm going with 11.5", either BCM or Ballistic Advantage. Will be using Silencerco ASR Flash Hider. Eformed Form 1 late June, so buying parts as they go on sale. Main items outstanding are barrel & rail.