Similar to the M500, except for the safety location which is a cross-bolt style behind the trigger. The action tube assembly is welded to the fore-end so you cannot swap them out as easy like the M500. Barrels are also not ported like the M500 field barrels.
Rem 870 has a steel receiver as opposed to the aluminum alloy of Mossberg/Maverick. Depending on whether you get Wingmaster, Police, or Express, you will get varying levels of finish and fit.
Personally owning both an Express and current M500, I prefer the M500 to the Express because of the weight and ergonomics. I like the 870 as well, but I'd go with a Wingmaster instead of the Express, so I plan to eventually own both, and you will too one day.
All in all, this isn't a question of which one, but "when" will you own a Mossberg and Remington. It's like an itch, you buy one, and you hear about the other after your purchase, and to cure the itch, you obtain both...