There are a couple things that tend to get lost in the caliber debate that are important to keep us all grounded. And btw, I'm not disagreeing with anyone above. There really is a surprisingly good amount of useful and valid information here. I love reading this kind of thread because I learn more every time. So I won't argue with anyone. This is more of a perspective comment when it comes to caliber.
We hear the caliber numbers bandied about and each have our own mental images that come to mind. Something to remember are 2 things. First, a .40 S&W is only 1mm larger than a 9mm. Bullet diameter wise, it's still in essence a 10mm bullet. The effective difference between 9mm and 10mm in creating wounds is pretty minimal. For more perspective, that's a difference of 5 one-hundredths of an inch difference. Under expansion, the initial diameter of the bullet is really unimportant. Some hot 9mm can actually expand more than standard .40. And a hot .40 can expand more than a standard .45, etc, etc. That's why the full cartridge and load, the total package, can be more important than the caliber. And also why pushing a JHP beyond it's design (really hot rounds) can actually make things worse. It's possible to ruin the effectiveness of a .40 by pushing it beyond it's design. That goes for any round really. The point is, we should avoid the cliched ".40 is bigger so it's better" mindset. (Not accusing anyone here because I don't think anyone has actually said that in any way.) "Better" has little to do with the caliber and more to do with the shooter, the load, the expansion of the bullet, etc, etc. Caliber is the bottom of the list of priorities.
Second, the gun community can too easily fall into the trap of "kinetic energy." This is a great area for manufacturer's to boast and sell and market. But when you really boil it down, the number is less than impressive. For instance, I'm not picking on SouthernBoy I just happened to use the Gold Dot he mentioned as a common point. Nothing he said is wrong. That 165gr Gold Dot. It's rated at 484 ft lbs at the muzzle. That's an impressive number and a lot of people see that and say "WOW" or whatever. And it's a good number. But for perspective, compare that to the average punching power of the average non-trained male. If you were to test your punch power (not being a professional boxer or even a weight lifter) you would find that the average non-trained male can punch with a power of between 250-350 ft lbs of force. Larger guys can push closer to 500 ft lbs. A professional boxer can punch as high as 1000 ft lbs. Now, what does that mean? Well, have you ever been punched in the chest by an average guy and flew back 20 feet? No. In fact, after being shot by modern rounds, many people state that they didn't even know they were shot at first. That's because "400 ft lbs" in a small diameter package isn't really that much force on a 200+ lb man. Now remember above I noted the 484 ft lbs. Underwood ammo makes a 9mm +p round that is rated at 467 ft lbs. That's high for a 9mm. Actually, they make a +p+ rated for 501 but I've heard that the higher speed is causing the gold dot they use to fail in the +p+ round and penetration is suffering. Anyway, lets compare the 9mm above to the .40. The difference is 17 ft lbs. If 300-400 ft lbs is barely noticeable to the average person, 17 ft lbs is nothing.
Now I'm not arguing, "See the 9mm is better." Quite the opposite actually. I'm arguing, there is no "better." Modern ammo and modern handguns have become so close that the caliber IMHO has become irrelevant. So to be honest, why you chose the caliber you choose is pretty much equally as valid as why someone else chooses a different caliber. Whether it be, I want the most common, I want what the FBI uses, I want what my local police use, I like the flat top on the 40, I like pretty shiny nickel.... Doesn't matter. It's all equally valid.