I am a waterfowl hunter and hard on shotguns. Neither the 500 or the 870 as they are made now would top my list if its an every day use gun. I have a 1990 870 and love it, but the new express line is cheap. I would vote the 500 over the 870 express any day. I have a 500 from '92 that the daughter uses for waterfowl and I used in the past and it works, but the safety has had issues and needs to be oiled. As I said I am hard on my guns and it sits in the pouring rain. Plus the 500 can hold 5 - 2 3/4" shells in the magazine with the plug out.
If you wanted a quality pump I would look more to a BPS or a Nova or something like that. BPS has bottom ejection which is nice in confined areas.
The 500 is the only shotgun I have ever owned for 25+ years. Great gun, great price. The safety location is the reason I went with them, and I have never looked back. I just think the safety is in a better position and I'm less likely to disengage it by accident. It's also more obvious to the eye as to whether it's on or not (in my opinion). Both are great guns - really comes down to safety location preference.
buy both with the intention of selling the one you like least, and then in 5 years you just keep the one you don't like in the safe as a decoration and you don't ever sell either.
I own both, 500 worked perfect out of box. Bought a 870 for my wife to try skeet first time out would not eject shells after three shoots. I have to send back for warranty work will take a month, Good customer service but WTH, They told me they have that problem with 1 out every couple of hundred
I like the 870, but when I was new to SG's I did manage to not insert a shell far enough up into the mag. It popped back out, tying up the action, until I was able to take the spine of my knife and push it in far enough to get loading gate depressed. Quite some time. In a firefight I would have been done. Won't happen with a Mossberg. Lucky it was a local deer hunt, worse case is drive home. That 870 is a part of the HD plan, but I know about the ability of it to jam and how to correctly load it now.
I have an 870 and my son has a 500. 870 has a 3.5lb trigger and the 500 has a 2 stage with about 5 1/2lb total. I threw the trigger gauge on it and the first stage was about 2lb.
I will say, my friend got the 500 combo last week with the scope and I shot it offhand at 100 yards once after zeroing it and hit a 5" circle so I'm eager to work with him to test some loads. Made me jelly he got it for $320 thanksgiving week. His combo had the cheek inserts which was nice how he could add more for when it was scoped.
I realize tyere are some nuances, but they have it already, its a Maverick 88. Had both the 88 and 500. Prefer in the 500, kept 'em. Sold the 88. So nice to have choices