As a result of being far too close to (and sometimes involved in) many armed encounters in a civil war situation in another country, I decided early on that 9mm. was NOT a dependable round for self-defence. I saw far too many cases where 1980's-vintage hollowpoints (not the +P and +P+ rounds of today) simply failed to stop a determined attacker until he'd done major (sometimes terminal) damage to the shooter. I'm afraid that even with the advent of higher-power loads, I retain a visceral distrust of 9mm. Parabellum as a "fight-stopper". I'll use it if I have to (particularly in smaller guns such as the Kahr PM9), but I won't like it.
I've standardized on .40 S&W and .45 ACP as my "carry" calibers in semi-autos, and .357 Magnum in revolvers. In very light snubbies, I'll use the FBI load in .38 Special.
I will never, under any circumstances, trust a round of less power than 9mm. Parabellum or .38 Special as a primary fight-stopper (although they have their uses in backup guns). Again, I've seen what works "up close and personal" - and the small stuff just doesn't cut the mustard... Sure, these rounds will kill anyone: but they won't necessarily STOP them, and it's really, really hard to get a CNS shot or two in the heat of the moment, especially with movement, noise, turmoil and panic in the air! I want something that will deliver as authoritative a "smack" as possible to my opponent.
I know there are many who will disagree with me, and that's fine. However, on the basis of far too much experience (which I would rather not have had, thank you very much), I'll stay with the "bigger is better" school...