Assuming you're hunting with a rifle and are right-handed, your left ear tends to be the one that will have the most hearing damage. Your right ear is nearly in a line behind the bore and the noise from the muzzle tends to cancel a little bit in that area. In addition, your head "shadows" the right ear slightly.The left one about half way in...
If you're going to take the approach of putting in one plug, the one in the left ear is probably going to be more use to you than the one in your right ear.