The Accurate 4064 has a similar burn rate to RL15, which the Nosler reloading manual lists as a very accurate powder for the 6.5 Creedmoor (on the cartridge description page). Ramshot Big Game's burn rate is a little slower than Accurate 4064, so between the 2 powders, I'd lean towards Big Game. Looking at their online manual, velocities also look to be about 100fps faster with Big Game.
That said, I personally don't have experience with either of these powders. I do reload for a 6.5 Creedmoor gas gun, and I use VV N550, and H4350, and both of these powders have slower burn rates than the powders you listed.