All arguements aside, I'm am a die hard 870 guy. HOWEVER... I have yet to hear of anyone wearing out a Mossberg yet. They do feel a bit cheap to me, but I will also answer that so does my express compared to my 870P.
What you NEED to do is go to the gun shop and physically handle both guns. Whichever feels right to YOU is the one you buy. The Mossy might feel cheap but enough enforcement agency's around the world probably have something to say about that. The real world fact is that altho both have serious downfalls against them, they both always go bang when required. Also note that the safety placement, being a preference only issue is a valid concern to look at. Gather as much info from everyone here, lol there's a lot of it. but don't write either off untill you handle it. And for what it is worth, $90 is not alot of money to save if it lasts a lifetime(As the all probably will)
My FABARM, on the other hand is the most baddass piece of equiptment going. Unfortunatly I traded it to a roofer to do my roof...priorities.