From my reading, the Internet consensus is that the Remington 870 is the best damn pump shotgun ever made. I've got an 870 Police, model
4901. I also just bought a Winchester 1300 Ranger Compact for my GF to shoot. It seems a good gun, although we haven't shot it yet, but it isn't as "industrial strength", "heavy duty", as the 870P. I recommend that you get the best. Get a Remington 870 Police. You will have the top of the line Combat pump shotgun. If it costs more, save and pay it. This gun is solid and will last beyond your lifetime.
Every 870 has a steel receiver, and the 870P (I'm not sure about the Wingmaster) has an aluminum trigger guard (not sure on the Express trigger guard either). The Winchester 1300 has an alloy receiver and a plastic trigger guard. That plastic looks really cheap, and it's the one thing I dislike, looking at and handling the gun. One of your other options is the Mossberg 590 series. If you want one of those, and you want a home defense gun, look into the 590A1 which is more solid than the standard 590 models. With the 590A1 you even get a bayonet lug. I used to have a 590A1 but my current Combat shotgun is an 870P.
For more opionions and advise, check out
Shotgun World and
The Firing Line, among others.
GL