I have nearly sold off all my shotguns because they don't get used much. I have a 870 12ga on permanent loan from a family member. I have a Mossberg 600CT 20ga that I earned as a teenager by mowing my grandfather's lawn. I have on permanent loan a bolt action 410 that was my grandmother's. Of the 3, I have not shot the 870 a single time in the 6 years I have had it. I have not shot the 410 more than a dozen times in my life. That 20ga is worn ragged but keeps on going. The only thing I can honestly say I would buy in a scattergun that I would use is a light 20 3" O/U with choke tubes. I want a tubed gun so that if I need to, I can shoot heavy loads at turkey or slugs for deer.
Deer, Turkey, rabbit, squirrel, dove, quail, pheasant, home defense, games...yeah I think the 20 is a great gun. In my book I prefer 20, with a close runner up in the 16. If the 16 were better supported in ammo, and was built on a true 16ga frame to reduce weight rather than use a 12 frame I would probably flip that preference. If i run across a 16 double before a 20 double I might have to start reloading plastic hulls.