The first gun I ever bought was a 9mm pistol for home defense and all around use. I don't hunt so I wasn't really looking for anything other than plinking and home defense.
The second gun I bought was an 88 Mossberg. I put a short barrel, an extra 6 round holster on the receiver, and an extra 5 round holder on the butt-stock. The magazine under the barrel will hold 5 I think.......so I have 16 rounds of 00 buck. Over-kill???? Not if I have to barricade myself in a room and hold them at bay until the good guys get there.
I'm really pleased with this shotgun. It's worn from use - I bought it used-but that just seems to make everything work better and smoother.
About a year later, I got a black 870 for Christmas. I did basically the same thing to it as far as setting it up. I think it will only hold 4 rounds in the factory mag, however, it is expandable unlike the 88. I would go as far as to say that the 870 is the nicer of the two but for some reason I really like my 88 and it spends the majority of the time next to the bed ready to defend the homeland. I don't like the front pump handle on the 870. You can replace them, and I think I did. I'm gonna guess my preference to the 88 is because the 870 was new, it didn't work as smoothly.
Either one is fine. The extra stuff is about the same price new and is easy to get. You can dress either one of them up. I would go with what will do the job for the least amount of money. Also, It seems like the release for the pump on the 88 is in a better location. I don't remember where but when it's in my hand, it's second nature. I always spend a lot of time with my home defense guns, so that it's just second nature.
Good luck!
edit: i see them at flea markets, locally and you might try gunbroker.com (will have to ship to an FFL but it isn't a big deal like i thought it would be)