If I wanted a home defense shotgun / and I don't - because I depend on my 1911's for personal defense...but if I did ....I'd look at a couple of different options ...over an 870 or the Mossberg offerings... neither of which would get my attention...:
a. in a pump gun ....Browning BPS all weather high capacity...list is $ 800 ...but I think the avg price is around $ 650.
http://www.browning.com/products/catalog/firearms/detail.asp?fid=011B&cid=012&tid=262&bg=x
But honestly, if I wanted a fighting gun ....I'd look at the Benelli M-4 ...as a much better option ...they're around $ 1,850 or so depending on how you want them equipped / but often in guns you get what you pay for - in my opinion. But its a solid gun / similar gun to the one used by the US Marines - good reputation among the Marines I've talked to in my son's unit.
http://www.benelliusa.com/shotguns/index.php?specs
Benelli offers their pump gun / the Nova in some tactical configurations ...and if you go that route, look at one that has the "comfort tech" recoil supression system in it. Firing slugs out of a fixed breech gun --- like a pump ---isn't that much fun ...which is why I'd go with the M4 as a semi-auto / much faster follow-up shots - much less recoil than a fixed breech gun.
There are a lot of others on this forum that can discuss "fighting shotgun tactics" with you - with way more authority than I pretend to have ...but any decent shotgun, if it will cycle the ammo you choose to use / you can take the "hunting plug" out of the mag ...and admittedly it might still have a 28" barrel on it ...but its still a 'defensive shotgun' - just maybe not an "optimal" fighting shotgun .../ but are you thinking about 'defense' - or a shootout at the Ok Corral ... / I don't think many civilians have much of a real need for a "fighting shotgun" ...not that you shouldn't buy whatever you want ...I'm just suggesting that you think thru where you're going with this purchase. In many police depts --- where they used to grab that defensive shotgun years ago ...I think a lot of them are thinking they have better options today .../ higher capacity handguns - freeing up their other hand, etc....
Based on what I read / classes I've taken on defensive shooting / tactical defense shooting ...its all about shot placement ...and the expectation is its really going to be over quickly ...like 5 sec's quickly .../ so a double tap out of a 1911 ...might be all I'll ever need ...and if necessary, I can fight my way to my gun safe...and my rifles and shotguns - and higher capacity handguns, etc.
But buy what you want ...at whatever budget you have ...and train with it often - and by that I mean at least twice a month or more !