Might there be a latter day Gyro Jet?
That's my first preference.
Minimal recoil. Laser targeting.
You can pack more intelligence into the round than you know what to do with.
I was deeply impressed with a report I saw a long time ago. The army needed something like six kinds of mortar rounds. Flare, high burst, low burst, ground burst, delayed burst, etc. They cut it down to two kinds of mortar rounds by putting a dial on them so you just choose the kind you want. And that improved the logistics a whole lot. Instead of having to provide the right amount of six different items, they only had to provide the right amount of two items. A little extra cost for each mortar round was completely worth it.
Ideally you'd have a gyro-jet round that blows up soon after it hits something, using whatever remains of its propellant. Past a preset distance it retro-fires and uses as much as half its propellant to slow down. You keep them preset, but if you have time you can set them for what you want. So to hit a spacesuit it might be better to blow up or burn fast when it's about halfway through the skin. For flesh you might want to wait a little longer. Or there are times when you wouldn't want it to blow up at all.
You'd have it set to the most likely need because in an emergency you wouldn't have time even to press one button to change it. But if you *did* need something different when you had time to think, you could get extra flexibility.
The downside is that the rounds themselves would be more expensive, and also you would be betting your life on high-tech expendables. You can't test an individual round ahead of time, you have to trust that it will do what you need it to based on the reliability of the previously-shot rounds you know about.
When I think about the goals, it looks like the most important thing is to have a gun that looks intimidating. When the sort of fool who might pull a gun on you looks at it, he should think about getting shot with it and being dead. A gun that does not look threatening is a bad gun.
So the Desert Eagle is good on that score. People don't know what kind of ammo it has but it's big and shiny and it looks real real dangerous. Most fools won't think that they can get three shots before you can get two. They'll think that if it hits them in the chest they're dead, and if it hits them in the hand they'll lose a hand if it doesn't kill them. If your primary goal is to not have idiots pick fights with you then it fills the need. (Not so good if you're an idiot who picks fights with people....)
A little gun that shoots 50 flechettes has a disadvantage on that score unless enough good stories have gotten out. A few videos of people getting turned to hamburger with them would convince most of the fools -- but not all.
So if you want a little gun, it might make sense to have a great big gun too, as idiot repellant. Particularly if you're left-handed, you could have a big gun or a fake big gun on the right....