If it is that small of an apartment then I would actually suggest a shotgun over a handgun. A .357 has the capability of going through a person and still penetrating a few walls if you shot them at close range. And if you miss it could go through several apartments still holding enough energy to seriously injure someone.
I also believe a shotgun would be easier to shoot well than a small pistol. I don't suggest getting a small barreled .357 and sticking it in a dresser drawer with very little knowledge of it's operation or how to use it. You would be better off with pepper spray in my opinion. Getting a handgun would require practice and possibly training in how to shoot and use it effectively. And then I still think a good shotgun would be more effective. It would still require some practice, but not near as much to be proficient with it.
As far as the handling of a shotgun vrs a handgun in an apartment, I don't suggest walking through the house trying to clear it like an officer would anyway. Unless you have training in how to do it properly, and then it's still risky. Stay put, call the cops and tell the intruder you are armed and the cops are on the way. Let them come to you, don't go after them.
An 11-87 in 12 or 20 gauge could easily be handled be either of them, and with the right loads and a tight choke it would be devastating on a human target and reduce the risk over penetration into existing dwellings. #4 turkey loads or goose loads are wicked out of a full or extra full choke at ranges under 10 yards. I have done tests with different loads and chokes at different distances. After these tests I would never use a pistol if I had a shotgun at my disposal.
Handguns are difficult to shoot well in controlled situations, let alone the stress of a break in or life threatening situation. Have you ever seen the videos of cops shooting at suspects at point blank ranges, they can empty whole magazines and never even hit the suspect. And these are trained professionals, not some guy and his girlfriend that bought a magnum six shooter and stuck it under their mattress or something
. Something to keep in mind anyway.
Paul