"golddigger14s",
I have a Mossberg 500 that came with 2 barrels as well--an 18" "home defense" barrel, and a 26" ported barrel with interchangeable choke tubes (not rifled, obviously). I use the longer barrel with a "skeet" choke for busting clays, and the 18" barrel when it's at home.
The Remington 870 was high on my list too, but ultimately I went with the Mossy because a local dealer was able to get me a much better deal, and it was available in a 2-barrel combo with wood furniture, whereas the 870 only came in poly furniture for the combo gun...
Conventional wisdom for home defense is that you load with 00 (double-ought) buckshot. There is, however, significant opinion "out there" that #4 shot is more effective than 00 because the #4 pellets are of effective size and there are more pellets in a #4 shotshell then there are pellets in a 00 shotshell.
I suspect that either will be highly effective in a home defense situation.
The "00 buck vs. #4 shot" argument is nearly as old as the "45acp vs 9mm" argument, and equally as heated...
Personally, I have stocks of BOTH kinds of shells. I keep #4 shot in my Mossy for home defense, for 2 reasons. One, they are 2 3/4" shells, and have a little less recoil. This gun is sometime available for my wife and stepdaughter (when I'm not home), so I thought #4 shot would be better for a multitude of reasons:
1) less perceived recoil than 00 buck
2) less worry about over-penetration in the thin modern-construction sheetrock wall of our home,
3) they fit one more round in the tube than 3" 00 buck shells.
And I think those are the three big arguments I've heard for #4 shot over 00buck. The overpenetration issue is VERY important for me, because of the way our house is designed and built.
But if I were home alone (no family and no room-mates) and the "Zombie Apocalypse" were going down, I'd be loading up with 00 Buck,, and have a box-worth in my pockets to boot...