I may be biased since I have owned Mossberg 500s for pretty much my entire adult life. I also dislike how the bolt and everything comes out of the 870 when you remove the forend, although that does make it a bit easier to get to doesn't it. Given the QC issues out of modern day Remington, I'm not sure how these stack up to the older 870s either.
Really I think they're both probably good guns and I wouldn't be afraid to run either one. I have to give the slight edge to the Mossberg for capacity and the location of the safety ( which I think is perfect). Although I would almost definitely pull the stupid strapped corncob forend and put a Magpul on it.
I have/am giving serious consideration to picking one of these up. Mostly because I see some utility in a 12 gauge with a 14" barrel. As usual though I'm like Doug in the animated Pixar film " Up". "Squirrel". In the next couple weeks I'm going to get one of those Black Aces 18.5" semi autos. They come with a "Raptor" grip AND a full stock. I haven't decided if I'll go with the walnut stock or the synthetic. The capacity is 6+1. For $400 it's impossible for me to say no. I ought to buy about 6 of them and give them out as Christmas presents. By the way, I know a guy who bought one and it runs flawlessly. Obviously I would mod it a little bit. ;-)