Revolver.
Joe Biden recommends the shotgun for beginners. Sorry, the shotgun is absolutely the wrong thing to hand to a beginner. It is hard to hit with -- the pattern doesn't spread out to fill the room. Shotguns are nasty, hard-kicking guns that require plenty of instruction and practice to use effectively. Shotguns hurt people, and turn them off of shooting. Here is one of the many videos mocking Biden for recommending shotguns for beginners. https://youtu.be/jafkVM-jnbE
Carbines are much easier to use than shotguns, but much harder to use than revolvers. Think Jessica Lynch. She said her gun "jammed". Right, before firing even one shot. She didn't know how to load the damn thing, and/or she didn't know or didn't remember that there is a safety switch on the side.
For a person who wants a gun in the house for self-defense, and will go to the range once or twice for familiarization, but will not become a hobbyist/enthusiast...revolver.