If the AR-15 is in .308 I think I would grab that one. But, there’s a reason God gave you two hands.
I think the AR-10 comes in .308
DPMS and other make a big block version in .308/7.62mm NATO. Armalite makes an AR-10 of the same size, but slightly different dimensions. All the usual AR attributes are there such as modular construction. The newer DPMS Gen 2 .308 rifles are a lot lighter than the first ones, barely heavier without ammo than many AR-15s.