For a general purpose shotgun, I'd look for a pump action with 26-30" barrels, vent-ribbed with a screw in chokes that are rated as good for both lead and steel shot. While you can sometimes get some nice older shotguns at decent prices with fixed full chokes, they do not always handle steel shot very well and are too tightly choked for most upland hunting. You'd want to have at least 3" chambers to handle steel waterfowl loads. I have a Mossberg 835 which has 3.5" chambers, and while I'm happy with it, many of the other 3.5" chambered guns (including the 870 Express Magnum) do seem a little to weighty for any hunting that requires walking far with the gun, such as chasing after grouse and other upland game. On the other hand, the 3.5" chambers are handy for me, since geese regularly show up in the places where I hunt waterfowl, and I might find it handy for when I take up turkey hunting. If I were on the market for an all round shotgun though, I would certainly want to handle anything chambered for 3.5" before purchasing one, and would quite likely opt for a 3" gun instead.
The 870 Wingmaster is a nice shotgun that should serve you well for the rest of your hunting career. It has many milled parts, unlike the Express model which uses more cast and machined parts instead. The latter shotgun weighs considerably more and might be a bit heavy to carry in the bush all day, whereas the Wingmaster seems better suited to such a role. And of course, the nicer wood and finish on the Wingmaster gives a nice touch, even if the matte finish on the Express is better suited to waterfowling.
The Mossberg 500, 835 and 535 shotguns sell for about the same or slightly less than the Remington Express and have all the features of many more expensive shotguns. If I were looking for an all round utility shotgun, I'd consider these first. That said, paying a bit more for a Wingmaster would hardly be a bad investment, and I would certainly feel confident with one, having handled and hunted with a few of them myself.
Good luck with whatever you get!
Frank