i run a mossberg 500 stock right now. i wouldn't mind putting a pistol grip/stock combo on it in the future. it's a solid gun and i love it.
if you're looking for duty/three gun you probably want to look for an auto loader. i think there is a three gun category for pump shotguns though.
one last thing to think of if you're going to use it for HD. a gun that's tactical and kitted up with lights, lasers, sights, shell carriers, tube extensions, etc may not be the best choice for HD. i say that because in the unfortunate event you have to use it - while it is PERFECTLY legal to have a shotgun like that - a DA with a vendetta against guns may use that to try to get you in trouble.
a plain no frills/no mods shotgun will look a lot better in that situation. i'm all about exercising my rights. but sometimes just because you can doesn't mean you should.