I currently own both and like them both.

"Trusty Rusty" is my Mossberg 500 and I have had it for 21 years, and it has claimed more critters then all other weapons that I own combined. Pheasant, Quail, Chukar, Grouse, Woodcock, Dove, Duck, Geese, Turkey, Rabbit, Fox, Coyote, Squirrel, Woodchuck, and 1 deer. I have had and shot it so long it is an extension of me, I must have shot 10,000 clay pigeons with it. Not a single issue with that gun. I take Trusty out once in awhile still even though I own nicer now, and he ALWAYS produces. That gun has a bit of magic in it.

My Rem 870 is only4 years old and I have a 28" smooth barrel and a shorter fully rifled barrel. I "like" it, and with the fully rifled barrel and RedDot scope on it is a deer killing machine. I don't like it on birds as much as Trusty though. It doesn't cycle as well as the Mossberg and has been a little finicky with ammo. That being said, I think it has to do with quality standards at Remington, as my Father's older 870 is flawless. I have held "new" Mossberg's and they do not appear to be as well made as my old one. The Remington now is just my deer shotgun.

I don't think you could wrong either way, and while I want tolove all Remington's I have had to many issues with recent purchases across the board to feel confident in them anymore.