If I was going 308 AR, the only one I would look at is the LMT 308. Yes, I'm passing on dpms, rr, Armalite and even KAC.
As for a piston AR, no way. I'm one of those who's ran a couple of AR's to a thousand rounds without cleaning just to see. I did clean my tactical cool gas tube with every pull of the trigger...
DI for me.
But my 308 is and will probably always be a bolt gun. Though I did try an AR-10 for a spell.