mossberg v. rem
Coming up as a kid, the 870 was the gun,and a Mossberg was an also ran. Guys who wouldn't/couldn't spend the cash on a Remington bought the 500. Rems had real walnut, a blued finish, and bespoke quality. Mossbergs didn't have the same look. And there was the steel v. alloy thing. Who wants an alloy reciever when one could get real, forged US steel?
Since those times, the Rem has nearly priced itself out of the market, fielded a number of synthetic and coarse finished guns, and the reputation of Mossberg has grown, and their looks are not so different in the price range. And their is an ongoing debate over Rem quality.
One diff is that the Mossbergs are lighter, due to their alloy receiver. If your going to tote one alot, and not shoot heavy kickers too much (say a slug hunter or a turkey hunter, usually 1 shot deals) the Mossberg makes sense. An all steel Rem seems to soak up 3" and mag recoil a bit better and might make a better pass shooting gun.
Performance wise, they are likely locked.