I have been using my Remington 870 12gauge for over 20 years. I have since graduated to other things, but still use it a lot for dove and squirrel. If I were limited to 1 firearm, it would be an Remington 870 or Mossberg 500 with a deer and a bird barrel. Stick with 12 gauge. Finding a selection of 20 gauge ammo is a nightmare for me (my daughter has a 20gauge). If a Remington 11-87 with both barrels is available, you could go that route as well. If you choose a Remington, pay attention to the year it was made. As I understand it there was a period of time where the quality suffered. I still love mine and would buy another. If you can find a Wingmaster 870 you won't regret buying it.