I picked up my Mossberg 590A1 for $500. US Army issue-ghost ring sights, speed feed stock, 8+1, bayonet lug. I feel on a non-pistol gripped shotgun the Mossberg has far superior controls to the 870-slide release behind trigger guard and tang safety vs. a crossbolt safety as on the 870. If you want a pistol grip I feel the 870 is a better choice.
I keep Centurian buck and ball in the tube and high velocity slugs in the stock. 13 rounds of 12ga in a compact package. I shoot skeet with her occasionally as well, but always get my clock cleaned bc of the short barrel.