So, is the 9mm the round? And I'm not talking just for tiny CCW guns, I'm talking for the "go-to" carry round.
My daily carry piece is a full size Smith & Wesson M&P9. One of the reasons I went with the M&P is that the two largest law enforcement agencies in the county where I live (both the city police dept, and the county Sheriff's Office) carry M&Ps. However, they both carry .40S&W models, and I still stuck with the 9.
Why? The .40 has proven to be a great fight stopper, one of the City boys put two into a goblin's center mass a couple years back and he was done before they even got to the hospital. (This was after he'd be tazed a couple times, yanked the leads out, and been OC sprayed. Also had a known violent background, especially against LEOs.) So why did I go with 9mm Parabellum?
There a couple reasons. The first, availability. 9x19mm is the single most common handgun cartridge in the world by some accounts. Just about anybody that carries pistol ammo carries 9mm. To go along with this, 9mm is also noticeably cheaper than .40S&W, .40's pushing close to .45acp in price. I figure if I'm going to pay .45 prices, I may as well shoot .45. But I like to practice, so paying 2/3 the price for standard ball is going to win me over any day. 9x19mm is still the cheapest centerfire ammo I know of. It's pretty well agreed that shot placement trumps bullet type every time. More practice equals better shooting, and more consistent shot placement. Price is important.
The constant criticism of the 9mm comes from stories on the frontlines. Soldiers apparently regularly shoot tiny middle-easterners (really, they're little guys) with a full mag, only to watch them shrug them off like mosquitoes and keep coming. While I don't doubt this may have happened with a highly motivated and drugged up insurgent, I don't think the fault lies solely in the diameter of the bullet.
The US military has long limited themselves to FMJ (Full Metal Jacket) loads of
115 grains 124gr loaded to +P speeds. This load tends to go really fast, and the fully jacketed ball does not expand. Even if it slightly deforms it will be prone to over-penetration, and a bullet that goes through your target and continues downrange is just wasted energy.
I regularly shoot 115 gr. FMJ at the range. It's cheap and plentiful, and doesn't beat the shooter up. But when I leave the range, I switch back to 124 gr. JHP (Jacketed Hollow Points.) You can get 9mm loaded all the way up to 147 grain, but I like the 124 grain for the balance between mass and velocity. The 124s tend to travel faster, which can aid in more consistent expansion, which is the entire concept of hollow points. In my M&P, I can carry 17+1 of them (I always just carry 17 though due to WI's stupid laws.) If I can't take care of it with 34 rounds of that, I done screwed up. The data I can find for the rounds I have show a regular penetration of about 12" and expansion to over half an inch. I feel pretty confident in that.
So do I think 9x19 is the be-all-end-all of handgun cartridges? Maybe, but something better could always come along, and it may not fit your exact needs. Most importantly though, I trust it. I don't feel under armed when I'm carrying my gun (well, I'm much more comfortable with a rifle, but that's another matter.) It may not work for you, but it works just fine for me.