I have an old M500 with a plain 30" full choked barrel. I've recently however been looking at the various Maverick, Mossberg, Chinese production and Remington Express shotguns for some friends of mine that are getting into hunting and shooting, comparing prices and characteristics.
The Maverick 88 is fine, but in addition to the fact that it has a trigger safety, the fact that it comes with just the modified choke really reduces it's appeal to me. For about $60 more you get a Mossberg 500 with the tang safety, three chokes, ported barrels, and I see on the latest models, sling mounts that used to cost extra. The drilling and tapping of the reciever for scope mounting is another plus.
For just a bit more (about $300 and change) you can get combos such as the field barrel plus rifled barrel, or the field barrel (with all three chokes) plus a short 18" barrel with both pistol grip and regular butt.
The Mossberg 535 gives you the added option of 3.5" shells for just a tad bit more than a regular M500, while the field/rifled deer barrel combo sells for just over $300.
While I've shot and sucessfully hunted with a Remington 870 Express, the Mossberg gives you a lot more for the same money. The Express (or even Grizzly for that matter) weighs considerably more than the Maverick/Mossberg.
Some of the Chinese pumps (mostly 870 clones) are nice for those wanting a short defence/bush hunting shotgun, but I don't see too many combos out there for waterfowling.
I'd recommend at the very least forking over the extra $50-60 for either a regular M500 with three chokes, or get the SIR 500 combo with the field, 28" fixed modified choke and 18" Cylinder barrel. If you can fork out another $50-60 you'll have a combo gun (500 or 535) that will be good for a wide range of waterfowl conditions and other hunting possibilities. If you don't buy the extra barrel in the combo set, you'll pay quite a bit more to add one later should you change your mind. But at the very least I think that you should go for a field grade Mossberg.
Best of Luck!
Frank