Pistol is the way to go. I have a 16" carbine gas and it was a total PITA to get it to run reliably. Part of that is the bbl manufacturer I'm sure, and I bought it when the round was pretty new and bugs were probably still being worked out, but unless you plan on only shooting supers, stick to pistol length. I have a 10.5" Noveske barrel with pistol length gas and haven't had any issues with it, other than getting the damn gas block pin in.