9x19 is a good general purpose round, IMO. One that is jack of all trades, master of none. It is a good plinker, but more costly than .22. It is an adequate SD round, but not on par with 10mm/.45/.357 mag. It's primary attributes are the sheer number of guns chambered for it, coupled with being the least expensive centerfire pistol ammo out there. I own 7 9mm guns and shoot them all frequently. I have never fired at a human being, but they have killed many rabbits, praire dogs, etc. I keep a ton of 9mm FMJ ammo on hand because it is cheap and packs easy. In a SHTF scenario, 9mm would mostly be used as a suppression/cover round. More effective cartridges would be used when the threat is exposed.
I feel adequately armed carrying a 9mm, but much prefer my 10mm. At 791 ft/lbs, it is nearly double the power of a +P+ 9mm. I have developed 9mm loads that produce over 500 ft/lbs, but the only way to acheive such velocities was using 90 gr. JHP's, which are too lightly constructed to penetrate well at mach 1.5.