It really depends on the use of the weapon. On my "tactical" 870 aka zombie gun aka hd gun I have a light and a collapsable stock with a Shotshell holder on it. But the 870 wingmaster is stock accept a slip on Shotshell holder. Nothing is needed to make it a great gun.
As another poster questioned, what is the purpose of the gun? Since you mentioned the 590 which is in the special purpose defense category, look at the reviews for both guns for that purpose. There are several good video reviews on YouTube. Nutnfancy has a three part shotgun review. There is an almost infinite number of combinations of sights, stocks, barrel lengths, magazine capacities, finishes, and after market accessories. Have fun putting it all together.