Of all of the firearms related quarrels, none rival the argument over which auto pistol cartridge is best for personal defense. This is partly because personal protection is very important, partly because folks assume there has to be a single best answer, and finally because there exists no definitive proof that one works any better than another.
With auto-pistol cartridges a triangle analogy is appropriate because you’re trying to balance a three-sided equation. On one side of the triangle we have power, on another speed, and finally, capacity. This triangle exists because a human hand can only control so much force, because a bullet’s speed is what makes it work, and because if capacity didn’t matter we’d all be carrying derringers.
With the 9mm Luger, .40 S&W, and .45 Auto, you have three approaches to solving the problem. Each of these cartridges has its strengths and weaknesses. So, to better understand the solution, we need to look at how each cartridge interfaces with each side of the triangle.