You are getting good information, advice, and opinions in this thread. :wink:
I own both. I've been shooting 870s since 1972 but have only owned one for the last five or six years or so. I've owned Mossbergs since about 1978 (I have three now, one on long-term loan to my kid.)
The 870 is by far the better gun. The Mossy isn't a "bad" gun but the Rem is much better fitted and can be made to operate much more smoothly. Mossbergs rattle and shake, even when new, and there's not much you can do about it.
The Mossberg is by far the better value. It'll do anything the Rem will but usually at much lower cost. A used Mossy 500 is among the planet's best firearms bargains. You can still find them for between $100 and $200. Hard to find even a used 870 for under $200 anymore, unless it's a beat-to-hell police trade-in (still functionally sound, but will look like ass).
It's easier to put a mag extension tube on an 870. If you want an extended mag on a 500, you have to buy it that way, and then you can't put a "normal" barrel on it.
Mossberg makes a simply delightful "Turkey Gun." 20" barrel with screw-in chokes, and a vent rib. It is hella cool looking and goes great with a Colt Python or Diamondback on your hip. :wink: Remington USED to have something similar but I'm not sure they offer it anymore. The Mossy Turkey Gun represents an OUTSTANDING value if you want one shotgun for turkey hunting, home protection, deer (with slugs or buckshot), other upland game hunting, and even an occasional round of informal skeet (you will have to put up with "real" skeet shooters whining about the noise of your short barrel--they are not used to the sound of "real" gunfire). :lol: :lol: :lol:
Both are good guns. The 870s, especially the older all-steel Wingmasters, are GREAT guns. Let your wallet be your guide, you really can't go wrong with either.