Of those two choices, hands down the 6.5x55. Id seriously consider a 6.5 Creedmoor, as the selection in rifle choices seems to be ever expanding in this caliber.
I personally shoot 6.5x55 Rem 700, as one of my favorite rifles for hunting season, but by the end of 2020 I’ll have a 6.5 Creedmoor in the stable as well.
It’s nice to have the option of buying factory ammo.
