Tube.
As kozak6 says, it's really a "Saiga 12 vs. the world" thing, since there's really no other box magazine fed shotgun that has any meaningful supply.
I've used an 870 Tactical, I've used a Saiga 12. Own both. The S12 will occasionally nose-up a shell into the top of the chamber, jamming it. Requires retracting and locking the bolt back, removing the mag, reseating things, and then reloading. That takes some real time and attention, and if it happens in a defensive scenario, you're hosed.
I've never had the 870 fail to chamber something. While I like the Saiga and I do keep it set up for defense, if I reach for a shotgun to defend myself, I'm grabbing the Remington.