Hard to go wrong with the trusty 12ga.

I would suggest getting a 12ga capable of shooting the 3 inch shells, if you can...you can shoot anything from 3 incher's down to whatever but with a 2 3/4 inch chamber you can not shoot a 3 incher. No telling these days what you can and can not find.

Plus...with ye old 12 gauge you can provide yourself with a self defense weapon as well as a hunting weapon. WIth slugs you can hunt many bigger game critters...at close enough range, while maybe not the ideal thing, I'd think you could kill just about anything in North America. Slugs are fairly accurate out to 100 yards. With a rifled barrel, they can be very accurate. Bird shot, at close enough range, can take out two legged critters.

The most popular round, it seems, for self defense is the 2 3/4 inch with double ought buckshot.

I shot some 3 inch shells with four ought buckshot(not to be confused with number 4 shot even though they would be quite handy) once and was duly impressed.

Single shot, double barrel side by side or over and under, pump action, autoloader...many good variations of the shooter as well some configured to hold many, many rounds.