John,there's a few gigs of stuff in the Archives on these shotguns. A few high points.
Any of the Big Four will give good service for at least one generation of shotgunner. The 870 may be the most durable. It's the most popular for that reason and because it was the first GOOD pump that used stamped parts instead of machined ones like the Model 31 Remington or the Model 12 Winchester.
More aftermarket goodies are out there for the 870 than the rest combined.
All that said, the Winnie is a good shotgun.
Both are available with short or long barrels, choke tubes, rifled bores, etc.
The Winnie is a bit lighter(mixed blessing, kicks more all else equal) and costs a bit less.
With 8 million made, the 870 has more used ones floating around, and we can get a lot of value for a little cash buying used.
I'm gonna weasel out of which is better and invoke the McCRule....
"Get the one that FEELS Better"....