If I was starting from an absolutely blank slate, I would go 6PRC. But I have decided for me, the easiest choice is a 6/284. And thats because:
1) I have a standard boltface Tikka as a donor action already; and
2) I used to shoot a 6.5/284 match rifle, and still have my old loading dies. The FL die is a Redding bushing die and I have plenty of 6mm neck bushings I can use, and the seating die is a Wilson Arbour die, so I just need to change the seating stem to 6mm.
An extra bonus is that I can use Lapua 6.5/284 cases.
I am just debating if I rechamber a low round 6XC barrel I have already, or go to a lighter profile in a new barrel. But otherwise the decisions were pretty easy to work out.