As for every choice it comes down to what you want to do with it.
For home defense I went with a Mossy wholly based on ergonomics, I simply don't have to move my hand as much to operate the weapon. Course I wouldn't put a pistol grip on a Mossy due to safety position but thats me.
I have an 870 Express I use for skeet and hunting but the Mossy stays by the bedside.
That being said, both systems are solid and you really can't go wrong with either choice and I've never had any problems with either weapon. Hardest choice for me was 18" or 20" for the Mossy, nothing screams "wrong house mother ****er" like a bayonet equipped shotgun.