Pretty general scenario.
What would be my 'mission'?
Assuming I'm not part of the rioting group and I am at home a good pump shotgun would keep most critters on the right side of the door; I've got good fields and angles of fire covering all access points.
Out and about in the family vehicle my regular carry is a 45acp on the belt and a well tested AR style carbine behind the seat. The more open country I have to traverse, the greater the chance of finding a well used .30 bolt gun alongside.
Everybody will have their favorite brands and styles. For me it's more about knowing the gun will function when needed, hence the 'good', 'regular', 'well tested' and 'well used' descriptions.
If your follow-up is then "what ammo?", the answer is 'what works'.
You're here in a gun forum, accepted as a 'gun guy'. 45acp, 12 ga, 223win and .308/30-06 ammo is/are the most plentiful on the planet-I've got a good supply of my own.
Why do you need to seek advice on what should be obvious?
Bells and whistles aside, something that works (because you have tried it) in a popular (re plentiful) caliber/gauge is the only choice. Grab something and try it; if it doesn't work for you trade off for something else.
You stop when it feels right for you and that's a personal decision only you can make. Sorry, that's the best advice I've got. Sharing all my testing and success's or failures makes for a long boring and mostly useless story. It usually ends with a major manufacturer and my choice will draw immediate negativity from someone else who made a different choice or someone else who thinks they know more.
If name really makes that much difference to you I carry a Springfield (or sometimes a Smith, Kimber, Colt,Walther or Ruger), I like
Remington or Mossberg for short shotguns but have a Winchester, and several $$$ others, I've got AR's from several places (a couple custom) and I have Remington, Winchester, Savage, Ruger, and Weatherby well represented in the safe. All my guns are well tested-that's the most important part. Poor performers have been sent packing.