+1 having had experience with a Remington 870 Super Magnum Express as well as having several friends that have bought the same gun, and only 1 of them has worked correctly out of the box, I'd recommend staying away from it unless you want to do some work on it right out of the box, or send it to Remington and wait months.
The only Remington 870 I'd be able to recommend to anyone would be an older Wingmaster, but I think it would be hard to find one for that price.
The Mossberg would be my choice. You can get a nice Mossberg for that price. Another option is the Mossberg Maverick they sell at Walmart for $187. While it's not the fanciest gun out there, it seems to be a good shotgun for the price from the reviews it gets.