BenL
John Galt Speaking.
I have both and would recommend the 300BLK.
The Blackout is more standardized (as an AR platform), lighter, and more versatile. The brass will always be plentiful (cut down from 5.56) and can shoot 220gr subsonic (with a suppressor, very quiet) or 125gr supersonic. Even if you reload, the .308 will be more expensive. I use 42gr of powder per charge (versus 11gr for the Blackout) and once-fired brass is ~3X the price. Even the dedicated parts for a .308 AR (lower, BCG, etc...) are ~2X the price of a Blackout.
The Blackout is more standardized (as an AR platform), lighter, and more versatile. The brass will always be plentiful (cut down from 5.56) and can shoot 220gr subsonic (with a suppressor, very quiet) or 125gr supersonic. Even if you reload, the .308 will be more expensive. I use 42gr of powder per charge (versus 11gr for the Blackout) and once-fired brass is ~3X the price. Even the dedicated parts for a .308 AR (lower, BCG, etc...) are ~2X the price of a Blackout.