My research (which is extensive) indicates that there is very little difference in effectiveness between .38 Special, 9MM, .357 Magnum and 45 ACP rounds in defensive shootings. Some people swear by one caliber or another but after 20+ years of looking into the matter, including interviewing surgical personnel for their observations on wounded people, my finding is that it doesn't make a whole lot of difference what caliber is used the results wind up being very similar. I have had surgeons tell me that they cannot tell the difference in wound size between a .38 Special and a .45 ACP. I know this sounds wrong but that's what they say.
As I said, many people reject this notion, but this is what I have learned.
As for bullet type, I would always use JHPs for defensive ammo, but again, I'm not sure if there's really all that much difference. I am told the problem is that no handgun generates enough muzzle velocity to really deliver a powerful blow. Even the .30-30 Winchester, not considered a real powerhouse by rifle standards, makes the .44 Magnum from a handgun look pale in comparison.
There's just "something" about getting that projectile up over 2,000 FPS that makes a world of difference in the damage inflicted.
I know many replies will now follow calling me an idiot and insisting that the .45 ACP (or whatever big-bore handgun the writer favors) is the be-all and end-all for defensive performance. I used to think that, too, until I saw a guy weighing no more than 140 pounds absorb four solid hits to the chest from a .45 ACP and still run nearly 100 yards before collapsing.
I now realize that there is no defensive handgun capable of true "man-stopping" performance. That takes a rifle or shotgun.
Everyone is free to carry what makes them comfortable. If you prefer a .45 then by all means you should carry one. My usual carry piece is a 9MM (115 JHP +P+) and I am fine with that.