For me, where and how I hunt I aim for the base of the neck/high shoulder. Same as others have described, 99% of the time its a bang flop. You know you did it right when they fold up there legs and seem to "hang" there in mid air.
But that's for typical new England distances. When the distance stretches, my aiming point changes to center of the lungs, its a good target and quite a bit more margin for error. Under estimate distance and you still have lungs and heart, over estimate and it lungs ands spine, its a win win.
I am a bow as well as a gun hunter, with the gun I don't expect them to move after the shot. With the bow, the sharp blades hemorrhage more efficiently, so the bones are avoided for lung tissue.
I don't like head shots as I have hunted with a fellow that does this every chance he gets. I am sorry to say it has accounted for some LONG tracking jobs when he catches the fringes. My uncle is a neck shooter. While I never remember him missing, its also to high percentage a shot for my liking.
CW