Wow, this is a good discussion.
So, I guess I'll dive in.
Prsonally, my philosophy is that skill is better than a big gun, and that luck is better than both.
That said, it's obviously best to be lucky, skillful, and carry a big gun.
I honestly have to say that I think that .45 or .357 are just about the best of the common SD calibers...
BUT
how much better are they, really, than the runners-up, 9mm and .38 special? How do they compare to one another? Let's find out, shall we?
.45's most common "adversary," the 9mm, offers somewhat better penetration, and with well-made JHPs, gives a level of expansion that is only a few tenths of an inch smaller than a fully-expanded .45, if even that much.
As far as different platforms for these go, the 9 probably wins out. In general, it's going to come in guns that have better ergonomics, due to smaller grips, and in a weapon of equal size, it will almost always offer increased capacity.
.357's most common "adversary," the .38 special, doesn't offer aywhere near so great a level of penetration, but bullet-wise, is almost identical. .357 is also fast enough that it might actually cause a little extra damage based on sheer speed, but personally, I wouldn't bank on that. Some might say "Well, there you have it, the .357 is better because it makes the same bullets go deeper," but these people are neglecting to realize that well-made .38 specials, barring extreme circumstances, were already going deep enough to begin with!
Platform-wise, the guns are identical, but recoil-control witht he .357 will always be more difficult. This means that the .357 is really at its best either against a target who is wrapped up in a LOT of clothing, or in a platform of 30 ounces or greater, whereas the .38 is probably at it's best in a pocketgun, during the summer, when people are wearing less clothing.
What have we, here? You say that in the summer, your clothing gets lighter, and causes you to have to carry a pocketgun, but that during the winter, you can wear more, and hide a full-size .357? How convenient!!
Now then, let's do some cross-comparison.
Let's go .45 vs. .38.
We're now getting strikingly similar penetration, with the .45 winning out by a couple of inches. However, you'll notice something: Unlike with the 9mm, .38 special is often at its very best with heavier bullets, which can often expand a bit better, and hold a straighter path throught the body, due to their greater sectional density. This doesn't completely close the gap between the two, in terms of expanded diameter, but it does mean that the .45, in reality, probably isn't eyelash-batteringly superior to a hot .38!
Platform-wise, the .45 will give you more shots, almost every time, but usually won't fit into a pocket. This whole thing is beginning to look remarkably similar to the .357 vs. .38 platform situation I mentioned earlier.
.357 vs. 9mm is equally interesting.
With the .357, we're most definitely getting significantly better penetration, and the improved penetration and expansion characteristics of heavier bullets. The 9 just can't stack up. However, this doesn't mean that the 9mm is a poor round. Thousands upon thousands of dead men can attest that this little "pop gun" is a killer, in the right hands.
In platforms, the 9mm is the clear victor.
That Glock 17 in your duty holster has about half the recoil of a similarly-sized .357, at roughly two-thirds the weight! It's also packing literally three times the ammunition!!
Finally, let's see the clash of the titans.
.45 ACP vs. .357 Magnum: Lots of fun with some big, big guns.
.357 wins out in pentration -- no contest. However, once again, We must be reminded that barring extreme circumstances, like that burglar who remembers to put on a parka and a fur coat, in addition to the customary four layers of denim that we all know that burglars are wearing, nowadays, the .45 is probably going to give us adequate penetration, to begin with. Does this make the .357's penetration "excessive?" No. It just makes it insurance. The .45 trades this "insurance" for a big, fat bullet that will consistently offer somewhat wider expansion. Be reminded, however, that the .357's best loads are going to offer expansion that, once again, is only a few tenths of an inch, or so, smaller! Also, .357 is a smokin' round. It's probably the only round here that causes sufficient temporary cavity for that aspect of its performance to be a significant wounding factor.
In Platforms, recoil control might be an issue with either gun, depending on the shooter, the weight of the gun, and the ammunition used, so we'll assume parity between the two in that department. Capacity-wise, though, the .45 gets the nod. Even a standard 1911 is going to hold one round more than the average .357, and a Glock 21 is going to double that same .357's capacity.
So what does all this mean?
Well, to me, it seems to mean all of this:
1) Autoloaders still hold more rounds than revolvers.
2) .357 Magnum and .45 ACP require a little extra training to be controllable, but they offer better performance in the trade.
3) 9mm lets you carry a bottomless pit of ammunition.
4) .38 special, barring someone who has wrapped their body in JC Penny Catalogs, is basically a lightly-recoiling .357.
5) .45 ACP makes a big, wide hole.
6) .357, outside of acts of God, always goes deep enough to do the damage it needs to do, and from a 4" barrel, probably offers at least a slightly significant temporary cavity, which is something that the rest of these rounds most likely do not.
Conclusion:
They all have positives and negatives, but any one of these rounds will most likely do its job, in the hands of a capable shooter. In the end, it all amounts to personal preference.
Pick the one you like, and learn to put the shots where they need to go, and you'll do fine.