Stick with a remy or mossberg. I can swap barrels on my 18" tactical 870 and put a 28" barrel on , use choke tubes, plug my mag tube and take it hunting. versatility is key.
I recently bought an 870 from a fellow CGNer. Great gun. A Plain Jane 18" barrelled "tactical" shotty with none of the "tacticool" stuff like picatinny rails all over the place to tear up your hands or snag on everything. Just a few, very simple, additions to the basic stock gun - better recoil pad, extended mag tube and a "no jam" follower in high viz yellow to make it easy to check that the mag tube is empty. But the biggest and single most useful adaptations he had done to it: he got the 18" barrel threaded for chokes.
That right there turns a "home defence" shotgun into a genuine "all around" tool. Just change the choke tube in the barrel, and it's good for everything from home defence to big game hunting with slugs to trap, skeet or any kind of birds.
From tests many people have done over the years with a variety of shotguns, the principal advantages of longer barrels are: 1. smoothness of swing when tracking flying targets; 2. less muzzle flash with both it and the noise further from the shooter's ears; and 3. somewhat greater muzzle velocity, although this is only really noticeable when the barrel length goes below 16". That's it. As far as shot pattern goes, that is much more dependent on choke restriction than barrel length. For things like trap or skeet shooting or duck hunting, any loss of shot concentration from using an 18" instead of a 30" barrel can be compensated for by choosing a slightly tighter choke.
If I ever spend the money for a KSG, I'll want it to be as "all around practical" as possible for a shotgun, so I'll invest the extra $100 or so to have a good gunsmith thread the barrel for one of the better makes of choke tubes, and then spend the further $200 to $300 to acquire a complete set of those quality choke tubes in everything from "cylinder" to "extra-full turkey" and usable for lead or steel shot.
Actually, I'm already in the process of acquiring that set of choke tubes for my current Remmy. The choke tubes themselves should be a once-in-a-lifetime buy, so in future, I'll just have to make sure any new shotgun(s) have barrel threading to fit.