I bought a Mossberg 500 (new) back in 1976 and it broke down CONSTANTLY, as did all the Mossberg 500s everyone else bought at the time. By "all the time" I mean every time I shot a box of trap loads or game loads something was broken, literally. My gun, the four or five other 500s I knew of, garbage. They may (or not) have fixed the problem, but of all the Remington 870s I have (from 1964, bought used in late 1970's) to the "new" (used but looked perfect, about five years ago) Express, and all the others I still have, I have never had a single problem.
When a guy I know brought in the "hog lot 870" (farmer leaned it up in the fence, the pigs knocked it down and buried it in pig bubblegum. A year later he cleans the lot and found it), we boiled the bubblegum out of it (literally, there was no stock so just dropped it in the tank and boiled it), replaced the springs (nearly all worked fine! But it was 100% torn down, springs are cheap, so why not?) and new wood, reblued. Gun worked fine! It's a great shooter!
Owned or shot nearly everything out there, the only gun to compete with the 870 is the Win Model 12 pump/Ithaca 51 auto in my book. Don't like the Rem 1100 (auto), Ithaca 37 is good, didn't like the Win. 1200/1300. Don't waste money on other stuff, get a Rem 870, new or used you can NOT wear one out. Maybe a Browning BPS (basically a copy of the Ithica 37) might work too, they are nice.