ANY reliable repeating shotgun of at least 28 gauge that's well known to the user is a good choice here.
The hardware we love to debate about is the least part. A good shotgunner is absolutely deadly with his/her shotgun of choice and pretty darn dangerous with most any other.
Any shotgun you're shot until it feels like a body part is a good candidate for a defensive arm.
Let's look at the criteria.
One, it has to be trustworthy. Fires 200 rounds of duty ammo glitchfree.
Two, it has to be durable enough to still work in the worst conditions possible with minimal care.
Three, it has to be able to use commonly available ammo.
Four, it has to be comfortable to shoot. Comfort means more practice, means more proficiency, means more effectiveness.
Fifth, it has to be capable of being operated 10 seconds from a deep sleep, in total darkness, in cramped quarters while we pray the liquid running down our leg isn't blood. Because we may need to badly.
Ask the ghosts of NO if you doubt this.
An 870 is hardly ever a bad choice for any shotgun mission. So are 1100s, 37s, 500s 1300s, 11s, A-5s, ad infinitum.
Pick one and go shooting....