I personally run a 12ga Mossberg 590SP with combat sights, Israeli Combat Systems slide grip with pat 1913 rails to which is attached surefire illumination. The buttstock is hogue - I prefer the grip. Plus if, for what ever reason, there are casualties I have 12ga starlight flares to alert medical heli-evac to my location. The 12ga shotgun has a lot to go for it. Not only for personal defence but survival applications as well.
I find the ballance point is easy to grasp and comfortable to hold (just forward of the action when loaded). This is important because if you've been fighting through the bush with a rifle that is cumbersome to hold you will feel it in your shoulders and neck at the end of the day.
Most important. STAY AWAY FROM PISTOL GRIPS AND FOLDING STOCKS!
I've put about 800 slugs through this shotgun and I've never had a failure to feed nor have any parts or pieces come loose or fallen off. I maintain it religiously, always keep it clean and the internals greased up. I've fired this shotgun in the field without hiccup even with dirt and conifer needles fouling the action. The tubular magazine capacity is 8 rounds of 2 3/4" slugs and I can chew through that amount of ammo very very quickly with this fast handling platform.
I am completely convinced that this shotgun is the best bear defence platform in Coastal British Columbia. However, I'm not sure how she would handle in extreme sub zero conditions - probably not very well. Certainly I would not have the action greased up - I'd run her dry. Worst case scenario you can attach a C7 Bayonet onto these suckers.
I hear wonderful things about the Remington 870 as well, but my experience is with mossbergs. The Mossberg is criticized because the extractor is smaller than the 870. I think this is a mute point as the mossberg has TWO extractors (one on each side of bolt). The Mossy also has a plastic trigger guard but again I've had no issues what so ever with any parts and components. Quite affordable and durable. We have walked many many kilometres in the bush together and I have complete confidence in this shotgun.
Yours truly carrying the mossy
Yes, I am part Saskwatch