One man's perspective. I own both, but to me they are just for two different things. It's the same problem I have when I go camping in the middle of nowhere. Do I bring a 44 magnum in case I run across a foul beast, or do I bring my 9 mm in case I run across a group of foul crackheads?
I own a Smith 686+, and I normally see myself carrying this 7 rounder with 4" barrel as my in between, the best of both worlds gun, when camping, with a full box of ammo. The 357 carries enough butt to be able to take on large game(especially when teamed with Tim's Buffolo Bore monsters) while also being somewhat controllable enough for self-defense.
However, I would be lying if I didn't say that their have been more than a few nights that I've heard voices in the distance and wondering what kind of crowd was gathering and wishing then I had my CZ 75 with 5- 16 round mags.
There will never be an answer to your question I hate to say, never ever ever, because it will always come down to personal preference. Stopping power? 357. Large amounts of ammo? 9 mm.
I look at your 357 vs 9mm question the same as my shotgun versus my AR. I just got done posting at another site when asked what was preferred for home defense. While always thinking shotguns had limitations, as the years go by I see myself starting to lean towards a nine shot Mossberg tactical with number one buck. Leaning, not fallen over yet.
So my answer was this. For one, maybe two, not three people for sure, the shotugn all the way. For multiple the AR hands-down. So to answer your specific question from my point of view, for one, maybe two people, the 357. For multiple, 9 mm. But only in the perfect world where one can forecast the type of attack. But since there is no such thing, my choice would be the 9 mm.
I grew up always hearing whatever gun you shoot best with, and shot placement was far more important the number of rounds. I always had a tendency to let that go in one ear and out the other. I mean it was good advice, but I just didn't think it had a place in reality because most people just don't take the time to shoot a couple thousand rounds so they can become proficient with their choice of weapon.
Today? I can tell you hands-down, I'll take one well placed round over 10 wildly shot rounds any day of the week and twice on Sundays. But that doesn't really address your question because you can shoot a well-placed round with the 16 mag 9 mm or a 2 round Derringer.
So when it's all said and done, in my own personal world, I have decided to choose the "more rounds the better" over "stopping power" and here's why for two reasons.
1) Even till this day, the experts will tell you, LEO will tell you, that no matter how good you shoot, in the heat of the battle, in the craziness of the moment, things never go as planned and all your training can suddenly get thrown out the window and next thing you know you're shooting less carefully sighted and placed shots, and more crazy hysterical shots. It's one thing to target shoot, it's another thing to shoot with bullets flying back at you. Based upon this and knowing that many of your bullets are going to miss its target entirely, I want back up bullets.
2) I think WAY too much weight has been placed on stopping power anyway. I mean way too much. Too many arguments, too many debates, too many friends made enemies over the subject. "A" bullet is very powerful and very damaging, regardless of the size.
I grow weary of this bullet is more powerful than that bullet, this bullet does this in gel tests, that bullet does this to a piece of meat hanging from a rope, or a watermelon sitting on a post. That's just what caliber. Now factor in the weight, the velocity, hollow point versus full metal jacket. It's starting to all become blah blah blah to me.
Tired of reading how the 380 auto is not ample, and how people act as if those who use it are no better off than shooting someone with a paperclip and a rubber band, when every single day people get shot with it and lay dead from it.
It's a GUN. It's a BULLET. It can KILL. Leave it at that.
Talk to ANY individual who's actually been shot and they will tell you that bullets hurt and hurt bad. I'm not saying to run out and buy a 22, even though there have been tons of deaths attributed to a 22, as well as being the caliber of choice for professional hitman. I'm just saying they are carried and can kill just as good as a 44 magnum. Or go into any crime ridden area and you'll see lots and lots of lots of people carrying and lots of people being killed by 25 auto!
What I am saying is ALL calibers are good to go, because it's not the caliber that kills, it's the placement of that caliber that kills. And the odds of everything working out like you think, the odds of you putting a bullet where you would like to put it, are probably slim and none.
22, 25, 32, 380, 38, 9 mm, 357, 40, 45, 44, take your pick. THEY ALL KILL WHEN THE BULLET HITS WHERE IT NEEDS TO HIT. So I carry more bullets to increase the chances of hitting where it needs to hit.
Answer? 9 MM with high-capacity mags over a 357 for home defense. And lately I just bring both guns for camping