Good call, FamilyGuy! Sorry not to have elaborated on the Nova, Silversport, but I'll be happy to post a bit more on the topic. I'm sure someone else will be weighting in soon also, given the several Nova/870/Mossy threads running right now.
I've had all of these guns at one time or another: three M500s, two 870s and four Novas. The only pumps left in the safe are the Benellis. The different makes are all good guns in their own way, each with attributes that the others lack.
The M500 is by far the Chevrolet of the group: cheap, dependable, a bit rough, easily repaired. My first shotgun was a Mossberg. I wouldn't have a problem with doing any kind of shooting with a Mossy, and would have no problem with it as a primary defensive gun. It's not fine, but it is bread-and-butter.
The 870 is more like a Buick: been around for a long time, standard setting in its time, and a pretty good value for the money. 870 parts- both original and aftermarket goodies- are plentiful, and getting a spare stock or barrel to make your gun multi-purpose is child's play. If it's good enough for hundreds of local police departments, then there's got to be substance there, and you seldom hear stories of the 870 that failed in the clutch. 870 actions slick up nicely with use, too.
I'd equate the Nova to a Cadillac: it's pretty far up the "pump-gun" quality curve, is fully featured and has alot going for it. Novas have lots of good things about them, and a few things some folks just don't care for. The 21st Century styling is love-it-or-hate-it, and it's construction is such that shortening the stock is just about impossible. It's new, and relatively unproven in the test of time. It's largely plastic with a chromed bore, so it's much more corrosion resistant than stock 500s or 870s. Forget about accessory barrels- getting one costs almost as much as a new Nova. It's action is 3.5" magnum by design, and it shucks very, very quickly. You can field strip it in moments without tools. I've heard of people having magazine feed problems with their Novas, but I have one from each of the first three years of production and haven't had a single failure of any kind (operator-induced short stroke not included!) over thousands of rounds.
As far as pricing goes, they are all more or less in the same range: 500s around $200, Novas around $300 and 870Exp somewhere in between. As shotguns go, that kind of price spread is vanishingly small.
So, I guess the questions are, "what do you like?" and "what do you want?". Anyone who feeds you a line about how 'this one is golden and that one is crap' is, well, feeding you a line. Every shotgun type manufactured has it's exapmles that got past QC, but in my book every one of these is an excellent choice for durability and reliability. The only remaining choice is value, which is a choice you have to make for yourself. For me it's the Benelli, but I fault no one who chooses an M500 or an 870.
Let us know what you choose!
John