I take the best shot I can, given the circumstances. If I can't find a shot that I believe will be a guaranteed kill (hopefully, within seconds), then I don't take a shot, at all.
On Doe Pronghorn, I take a lot of head shots. Blowing up the brain case is an instant kill, and usually surprises the rest of the herd so much, that you can take additional animals while they stand there confused.
When I can't get one, or don't have confidence in a head shot, I go for the double-lung. Antelope don't have many large muscles on them. I can't afford to waste any meat, by blowing up a shoulder or the backstraps (spine shot). The double-lung works well for that.
You get multiple issues causing a quick death:
1. Bleeding into the chest cavity. (Hemothorax)
2. Air entering the chest cavity. (Pneumothorax)
--Those two complications diminish the animals ability to breath, and greatly limit blood oxygenation. In addition, it can cause irritation to the heart, and trigger heart spasms.
3. Blood in the lungs.
4. Loss of blood pressure.
--Altogether, you get: Dropping blood pressure, blood blocking airways, pneumothorax, hemothorax, and possible collapsed lungs (due to #1 and #2).
Where things get really "good", is when you use a bullet that causes a lot of hydrostatic shock. "Shattering" the lungs is a beautiful thing. Death is very quick, and anchoring them occurs even sooner (3-5 seconds). When you open them up, you have lung soup.
(Last year, I had it occur with a .277" 140 gr Nosler Partition that barely expanded, and only hit the lungs. Tiny entrance hole. Tiny exit hole. Ran about 50 yards*. Lung soup.)
*Remember, they're the fastest long-distance runner in the world, and the fastest sprinter besides the Cheetah. They can cover 50 yards in the blink of an eye.
For pretty much any other big game animal, I take anything available. Since I don't hunt Whitetails (any of the sub-species), that means I'm after Muleys, Elk, or Moose. On those animals, a spine shot, heart shot, neck shot, or anything else that seems like a good idea, isn't such a big deal. I can afford to lose a little meat, and don't hesitate to pull the trigger when I get a kill shot lined up.
"Such is the strange way that man works -- first he virtually destroys a species and then does everything in his power to restore it."