The only way to know what will give the best performance in your gun, is just to try various types of ammo.
Shotguns are kind of like .22s in that regard.
Maybe it's a Mossberg thing, but my 500 12 gauge is the same way.
I have both barrels, one a smooth bore, modified, and the other a rifled with sights.
Using standard ole' foster slugs in the smooth bore and trying various sabots in the rifled barrel, they both are about as accurate, with the same groups.
Any difference at longer ranges is more due to the lack of sights on the smooth bore than anything else.
Lock the doors, they're coming in the windows.