I got my first Mossberg 500, a 20 ga., when I was a kid. It has functioned flawlessly for many years.
A couple of years ago I got another one, this time a 12 ga. turkey gun with ported barrel and an extra full accu-choke. It's a great shooter. I bought a 18 1/2" HD barrel for it and converted it into a home defense gun and it handles 00 buck and slugs like a champ. Here's a couple of pictures of it in it's HD role:
One thing to consider is that while a Mossberg 500 is 5+1 for a total of 6 shots, it is not modular like a Remington 870 and cannot easily be expanded to greater shot capacity without changing out a number of costly components where with the 870 you just have to add a magazine tube extension.