I own both a Supernova and 870 express tactical, and shot a few other 870s over the years.
In my opnion, the Benelli is a higher quality gun, with better finish and smoother action.
I would stay away from the 870 express if i were you. The newer ones are cheaply built and i have seen one jam twice at the club, with the last shell stuck in the chamber so hard, it had to be hammered out.
I know the older 870 Wingmaster has always been of better quality than the Express, but i don't know if quality has gone down on them as well, so i would advise you to do a bit more research on it.
You might also want to check out the Browning BPS. They're good guns and in the same price range.
In the end, i would strongly advise you to try to at least shoulder any gun you are considering, and find which one fits you best.