It depends on what you want to do with it.
Home Defense?
I'd buy an Remington 870 over a Mossy 500.
I prefer the 1100 over both cause its a semi auto and I already have one I use for sporting clays.
Get an Over/Under for Trap/Skeet/Sporting Clays.
What do you have for clays?
My dad and I are planning on giving it a try this year, never done it before. I was thinking of getting a Stoeger Condor for cheap locally to get going without much $$.
-Jay
Condors are heavy and tend to break firing pins. They will not send you the parts to repair it. You have to send it in. They lock up super tight when new but get sloppy quick. Trap guns are expensive. Get a used Citori or a BT99. I actually shoot an Ithaca 600 Trap made in the 70's by SKB. I have about 6k rounds through it. Still locks up great with no issues. I bought it used for $650 and it locked like it was never fired. I put a Jones adapter on it and a kickeez pad. Fits me great now.
Truth be told if you dont intend to shoot every weekend any gun will work. Field guns tend to shoot flat and trap guns shoot on rise. Its just how you adapt to seeing the bird. 28" barrel length minimum. IM or Full choke. I shoot IM for 16 yard and wobble and my full barrel for handicapped.
I shot my 1100 with a 30" full choke barrel for 8 months and still beat up the birds. That gun needs lots of cleaning and maintenace though. I only use it for sporting clays now with a 26" barrel I can change the chokes with.