I've had my New Haven 600 (made by Mossberg), for close to 25 years now, the action is smooth as silk, can use any barrel or accessory that the 500 uses. Never had any problems with it, just need to get an 18.5" barrel (it has a slug barrel on it currently) and maybe a barrel for bird hunting.
I've also shot Rem 870's and they are very nice.
I've got my father's Browning A5 Featherweight (vintage around 1952, Made in Belgium)) and it is a sweet shooting shotgun.
It's what you prefer in a shotgun, if I had found an 870 for what I paid for my 600 I might have bought that instead.