M1A Scout / SOCOM is a LOUD rifle, so LOUD you would have to double up on hearing protection if you shoot in a closed bay, or a bay with a roof.
The performance of both is not in the same ball park do to the diff in calibers. The Ar-15 is faster in every respect for follow up shots. Yes even a .308 needs follow up shots.
So its up to you, you can get a real nice Ar-15 in .223, 6.8 or 7.62x39mm for much less then the cost of a rack grade M1A of any kind.