In my opinion, so much agonizing over the angle is unnecessary. I always tell new hunters, do the math if you know how. You'll probably stop worrying about it if you do. Having said that, the situation is somewhat different depending on whether I am hunting with a firearm or a bow.
With a bow, depending upon the distance, it is a good idea to aim a touch low if the shot is over 25 yards for the simple reason that a deer will react to the sound of the shot and when they do, they compress down before they launch to turn and run. Because they do that scootch, a high shot is often going over the top or stinging the backstrap. Also with the bow, a lower shot will fill the lungs more quickly and improve the blood trail for tracking. If you lung shoot an elk high, it will take a while for the lungs to fill and dump blood. A lower shot gets you a trail to track sooner.
With a gun, hopefully you are sighted in and know your hold-overs? Bullet drop and trajectory blend together at longer distances. So, if you are shooting inside the range of a relative flat shot, hold on your target. The bullet will get there and do the job. If you are shooting way out, your hold-over will be far more critical to get right than a few degrees of inclination. If you are in a stand or on a hill, it really does not play a big role.
And finally, buy yourself a good range finder that does the math for you. My Leupold is perfect for bow hunting and burps out the right numbers for me every time. I spend far more time thinking about shot angle and placement than the hypotenuse of the triangle.