I'd suggest both a .22 pistol and rifle and a shotgun. Ammo will be common & cheap, and in the case of the shotgun, versatile. The fourth really could be your choice, maybe a full size 9mm or a 5.56/.308 rifle of some sort.
I really can't strongly suggest the .22s enough. I've got a scoped Ruger 10/22 and a Browning Buckmark, both with bull barrels. They are fucking tack drivers and cheap enough to shoot all day long. I bring a lot of new shooters to the range, and they're always everyone's favorite to shoot due to their high accuracy and low recoil. In a GTFO scenario, they would actually be my go-to guns unless there was open warfare in the streets. 8 lbs for 1000 rounds is hard to beat.
Here is an opinion from a gun newb who did this 3 years ago. I bought an XD9 and I put my own AR-15 together. I also bought 1000 rounds of ammo in a sealed case.
In hindsight the only good part of the whole experience was the fun of putting the AR together. I rarely go to the range and I still can't figure out a reasonable way to shoot the AR. Firing one at an indoor 25yd range makes you feel like a moron.
Don't be me. Make sure you are actually going to dedicate yourself to the range time or don't bother.
It's the Ruger 22/45 for me with a buttload of ammo. That'll be gun number 1. Assuming I can start pegging tight groups at range, I'll move on to a 9mm and a rifle.
Now I gotta set aside 250 beans and find a good shop to do a blue card.
To money's point about the .22 pistols - I'd have to disagree. I also have a 10/22 and a Buckmark. Like I said, the 10/22 would be a go-to rifle for me but I can't see choosing a .22 pistol if you're limited to four guns. Hell, I'd take two .22 rifles before a .22 rifle and .22 pistol.
I'd gladly hump .45 ammo all over the countryside before I'd rely on a .22 pistol for anything other than plinking and target practice. Just my opinion.
Well, like I said, I want to work on my trigger pull and sight picture. The 22/45 is cheap and cheap to load, so that'll get the job done for me at the moment. If I'm still limited to 4 guns I can always sell it. By then, with any luck, I'll be comfortable and on-target shooting with a 9.