I have a Mossberg 500, was my first shotgun. Its a great gun, and the price is hard to beat. The biggest complaint I have about the gun itself is how noisy it is to carry. The tolerances on the slide are pretty loose, and it rattles quite a bit. For a stand gun, its not much of an issue, for still hunting though, not great.
This year I picked up a Remington 870, and from shooting it and getting it dialed in, I love it. Nice and quiet to carry, smooth action and very accurate. I havent carried it on a hunt yet, but have no worries that it will be anything less than expected.
The price on an 870 is a bit more than the Mossberg, but there are literally tons of them to be had used for a price more in line with a new Mossberg 500, possibly less.
Just my 2 cents.