I keep drafting posts in this thread, and then deleting them. Maybe this one will get posted.
I voted 5 rounds of .38 Spl.
Why?
I'm a revolver shooter who has practiced shooting 5-shot snubs for many years. I prefer the heavier bullet weights of the .38 Spl over the .380 ACP, especially when some of the better +P hollowpoints that have been tweaked and optimized for use in short-barreled revolvers are involved.
I know folks (LE and non-LE) who have favored using largish .380's, though. They use and shoot them well, so that's fine. Why not? I'm not responsible for
making their choices for them, or
using their choices for them. I don't have to agree or disagree with their choices, so it doesn't affect me. Their privilege and responsibility, including any and all consequences. (As it is for all of us.)
I once owned a Beretta M84 double stack .380 more than 25 years ago. I'd MUCH rather carry my similarly sized 3913, 3913TSW or CS9 single stacks. (My double stack G26's and SW999c offer the ability to carry 2-3 more rounds than those single stacks, too.)
Nowadays I own a pair of LCP's. I
only got back into owning the .380 ACP because I found I could carry them in tighter pants pockets (holstered) which wouldn't let me carry one of my J-frames. I have no use for a larger .380 pistol. That's
me.
The trade-off is they're still .380's, even though I'm using some of the best of the major brand JHP's available. (Of course, there's the .380 users who will argue that only ball ammo is useful, because of its penetration abilities, but that's another twist on the topic.
)
FWIW, when it comes to "pocketable" pistols and revolvers, I still place
my primary emphasis on the proper functioning of each, and the ability to make consistently accurate, controllable and (hopefully) effective shot placement of the first few shots fired. No "range warm-ups". The first shots fired in some demanding drill or training scenario doesn't get the option for excuses being applied. That means sufficiently frequent, realistic practice (and hopefully some initial and recurrent training efforts).
I'm less wrapped up about sheer capacity concerns. But hey, I carried a 6-shot revolver on & off-duty as a younger man, and considered myself equipped with a "higher capacity" weapon when I carried my Commander (7+1). My issued and personally-owned off-duty weapons have had "capacities" of 5, 6, 7, 8, 9, 10, 12, 14 & 15 rounds (with "+1" in applicable pistols).
Well, okay, once upon a time I briefly carried a 4-shot COP .357 Derringer off-duty (gift from my dad).
If someone already owns a largish compact single stack .380 of similar size (or larger) than some of the newer 9's? Let'em enjoy using it. Maybe they can shoot it significantly better, faster and more controllably than a 5-shot snub.
If they own both? Let'em use their experiences in shooting both, and make the decision for themselves.
Doesn't mean they can't continue to compare their experiences with both guns over time though. If there's a local handgun sporting/competition event (IDPA) available, maybe they could try using both guns in it/them, and see whether their experience changes their mind about which gun (if either) might be preferable, and under what conditions.
If they just
like one or the other? Well, that's a decision, too.
Tempest in a teapot. Pick one and work to master it. It's a tool. Some tools are better for some tasks than others, and some tool-users are better at using any tools than some other folks.