It depends. Usually, I'd say the box fed auto, because you can get a full magazine in fairly quickly, and you can shoot it pretty quickly.
But...
I would rather be equiped with a good pump gun (Or even better, that one Benili I think it was that was a semi auto, but still had the pump feature to cycle weak loads). An auto like the S12 is going to be run pretty much like an AK, because, well, its pretty much an AK.
If it doesn't have a Last Round BHO, I don't know about you guys, but I have a hard enough time counting my shots when I'm just at the range, so I wouldn't know the gun was empty until I pull the trigger and nothing happens. Thats not really something I would want to have happen to me in a gunfight. Even if your shotgun does have a LRBHO, that still means you don't know you need to reload, until you need to reload.
So for me, I'd rather take the handicaps of a tube gun, so that I can have the benefit of being able to top off the magazine when I get behind cover.
Chris "the Kayak-Man" Johnson