do I want large rifle primer or small rifle primer brass?
It depends. The original Remington brass is LR because that's what the parent cases were. Hornady and SSA are SR and supposedly stand up to repeated hot loads better. LR supposedly achieves higher velocities though and does better in cold weather.
I don't see that it matters much. 6.8 may be harder to obtain than I first thought. It's sounding like a lot of places are sold out of about everything. So you may not have much choice. I don't see that it matters a whole lot. Remington is generally the cheapest ammo anyway.