Like always, its about the risk assessment and what is appropriate for the scenario. It’s like the firepower vs mobility question, lightweight concealable IIIA vs IV in a tactical plate carrier with all your molle filled out and everything in between. And I suspect, kinda like firearms… you will end up buying more than one to fit different uses as there is no “best armor for all situations”.
If you live around riot areas, what is the risk there? I have not heard of rifle usage, but some handguns. Mostly they just beat/stab you or throw bricks. So if you felt that was a concern, some IIIA armor which protects you from the most common threat in that scenario which is pistols and its very concealable so you avoid being noticed in the first place. Some (all?) IIIA is also stab resistant. If you need to get through a crowd to get to safety, blending in is a way better option than shooting your way through. The armor just protects you in the small chance of being shot in the middle of the riots. This is IMO the most likely use case for armor right now is rioting and/or getting home past a riot area.
If a mass shooter incident is the primary concern, you have a 50/50 chance that the shooter has a rifle (from FBI stats), and about a 10-20% (IIRC) chance that the shooter is also wearing body armor. In that case, if you can make it to your active response kit, a rifle caliber firearm and III, III+, or IV armor is more appropriate than what is likely in your EDC loadout. Probably a large trauma kit too for when the shooting stops. It’s OK if its heavy because you won’t be wearing it for too long (although maybe some sprinting here and there )
If its for home defense, I’d say the most armor you can get. III, III+, or IV armor, weight doesn’t matter much since you aren’t traveling far. Home invaders have been shown to have everything from bare hands to AR15s and shotguns and sometimes also body armor.
Cost and shelf-life matters, IMO. As you mentioned this is stuff that will probably go unused for a long time (or maybe not depending on how you feel about current state of the nation). The other armor threads have a good run-down on pros/cons of each armor material type.
I don’t think body armor should be the first thing anyone gets. But if you already have firearms, you have ammo, you have accessories like lights and optics, you have some training… why not? After body armor, the next thing to complete the set is night vision, which is thousands of dollars