If target shooting is all you plan on doing with it then it depends on far you want to shoot, as you have already figured out. Me, I don't have or plan on having an extensive rifle collection so I went .308. If I need to use it on Zombie's or creatures with heartbeats it makes a bigger hole.
If you are not concerned about ammo cost go .308. Better to have the ability at longer distance if you decide you want to go that route.