The military didn't test anything, Mossberg was the only submission that met their requirements. Remington did submit their 870, but it wasn't accepted based on magazine capacity, as I recall. Based on the specifications and requirements it was apparent that the military had already decided on the Mossbergs before they even opened the testing.
For a hunting shotgun, any of them are fine. But for an offensive/defensive weapon, I'd take the Remington 870 any day, as long as it's not the express. It is not only reliable, but it is the easiest shotgun to clear a jam in. It is also the easiest to opereate if the shooter is injured and can only use one hand. It can be easily loaded in a hurry by putting a round directly in the barrel, which an Ithaca can't, and it is easily field stripped.
Mossbergs don't unjam easily and if the screw comes out of that tang mounted safety the gun must be disassembled to fix it. Then it takes three men and a little girl to put it back together.
I have an older Ithaca DSPS. The forend broke loose the first time I shot it as it was only spot welded on. Plus, as I noted above, to load it you have to place a round in the magazine then cycle it into the barrel.
