As for the "old slow and weak comment". Do a little search on the history of any cartridge, might surprise you. "Old slow and weak" was developed to stop drug crazed tribesmen. There maybe cartridges developed now that may do as good or better job.
But remember to respect your elders, "old slow and weak" has protected men in harms way, longer than most of us have been on this earth. Besides I resemble that remark......... Duce<><
Oh look, 45acp is in the lead. Old, slow and weak.... Just like everyone who voted for it.
I said 9mm because, to an extent, I'll take capacity over round size. With modern defense ammo, the 9mm will do the job just nicely, and I just can't say no to 17+1.
What about the .357 SIG? I personally go with the .45 ACP, but there are some very interesting stories about police departments that use the .357 SIG round. From what I have read these departments are finding that the .357 out performs many rounds on penetrating barriers and there have been several cases where one shot will stop a suspect, but on the other hand, when used in a good hollow point over penetration rarely becomes an issue, as most of the rounds are found in the body or are caught by the clothes. Supreme handgun round? I don't know, but it is an interesting round.