>Mid-tier AR-15 minimum with a high-quality bolt carrier group
>Generation 3 Glock 19 or one of the common well-reviewed clones, i.e. PSA Dagger
It's the most basic bitch loadout for a reason; it works. These are what you get when you finish the tutorial against bots and rank up to level 1. These are the way to go. The guns are everywhere, the parts are everywhere, info is everywhere, 5.56 and 9x19 are everywhere (until there's a panic, so stock up while the going's good.)
Both are extensively tested, both are extensively proven. These two guns should be your number one priority, ideally starting off with a Glock because you can have it with you in many more situations than an AR.
If you actually care about being able to reliably defend yourself and your loved ones in some manner of SHTF situation, STAY AWAY from special snowflake cool-factor shit like PS90s. Guns, like cars, are machines, and as such will never be perfectly 100% reliable no matter what. Going with a basic bitch 16" barrel AR with a carbine-length gas system means that if you run into any problems, there are decades worth of information on how to fix it, and if it requires replacement parts, they are affordable and readily available. No worrying about "Will this ammo cycle in my particular gun? Will I have to do tuning with buffer weights and springs? Can I get parts for this?" NO SPECIAL SNOWFLAKE SHIT UNTIL YOU HAVE YOUR RELIABLE, EFFECTIVE GUNS ALREADY!!! I CANNOT STRESS THIS ENOUGH!!!
SHTF situations are usually a long, drawn-out, day-by-day breakdown in quality of life and social cohesion. You probably won't wake up tomorrow without power and have to go kill and gut a deer to stay alive before you mount a Marvel movie final stand against U.N. tanks. It is much more likely that you'll still be going to work, going to the store, doing typical everyday things, but those trips out to town get a little more sketchy with each passing day.
This is why the Glock should be your first priority. You can take it everywhere with you, you can have it handy while you're in the car, if you have a baggy enough shirt you can conceal it even outside of cold months. You can't do that with an AR. If things come to the point where you need to have your AR with you all the time, things have gotten bad enough where leaving the safety of your home should be a last option. But if things do get that bad, you'll be very happy to have something more than a pistol.
Obligatory ymmv do your own research