I am not a fan of shotguns and I don’t think they are the ultimate home defense gun. Somebody asked in another venue about the difference between the 870 Express and the 870 police. Both guns are parts compatible but the 870 Police is marginally the better gun:

Parts:
Longer magazine spring to improve feed & function.
Heavier sear spring to generate a reliable 5-8 lbs. Trigger pull.
Heavier carrier dog spring for more reliable feeding.
Compressed metal trigger housing.
Machined ejectors and extractors.
No ISS (Integrated Safety System) key locking mechanism.

Quality control:
Higher quality control standard and inspection standard.
Built in a special build area of the factory.
All parts are inspected before entering the the build area.

Barrel:
Can except a magazine extension tube without barrel modification.
Barrel is locked down with a “ball-detent” in conjunction with the magazine cap.

Furniture & Finish:
High luster blueing or parkerization.
Recievers are “vibra-honed” prior to parkerization or blueing.
Shorter fore end (for compatibility with vehicle racks.)
SPEEDFEED stocks and fore ends.

As a defensive shooter what you would care about is the better parts and springs and the rest is mostly eye-wash. The police model is a little more expensive, but buying an Express and upgrading it is less likely to produce the gun you are looking for.