Unless you just want something different the 870 would be the better choice. There have been many reports about Benelli USA not having good customer service. It can be very hard to get parts as well. Also there aren't many after market accessories for the Nova either.
On the other hand Remington has excellent customer service and 870 parts and accessories are plentiful. I would look for an older 870, one that is at least 10 years or older. The steel receiver on the 870 is a big plus for me.
The Mossberg 590A1 18.5" barrel would be a good choice as well. It has a aluminum receiver but the rest of the shotgun is built like a tank.
I wouldn't even consider a TriStar Cobra because has been getting some bad press. Here is a review written by a forum Moderator on the TriStar Cobra Pump.
Product Review: TriStar Cobra Shotgun - TheHighRoad.US
GC