I had my cousins 887 for a month took her out ran her through her paces, the 870 is a better gun hands down. Parts of the bolt on the 887 are polymer as where the 870 is full steel. Also if for some reason if you end up unable to use on of your hands it's harder to work the 887.
The moss 500 isn't a bad gun but the 870 is easier to take apart, also you can get tons of different things for the 870 as where the 887 has limited after market parts available, the 870 is pretty much like a shotgun lego set you can have one actions but have the parts to set it up for home defense, turkey hunting, or trap shooting.
"come on you sons of b***hs! do you want to live forever?" Sergeant Daniel Daly, USMC, Belleau Wood France June 6th 1918
"You can be as mad as a mad dog at the way things went. You could swear, curse the fates, but when it comes to the end, you have to let go" Benjamin Button