Currently for me, the 870 is by the bed in case of an intruder. However if there was a disaster or SHTF situation, I would take either my Saiga 12g loaded with a 20rnd drum full of #4 buck or my .300 blk AR15. As far as raw firepower, I haven't seen many things that are close to the saiga 12g with a 20rnd drum loaded full of buckshot. I have tuned and used mine enough that I would trust it in a life threatening situation. I have put over 1.5k rounds through it and it is well broken-in and very reliable. Plus, it looks mean.
My .300 blk rifle is gaining my trust and interest more and more as I experiment with loads and see what it can do. Not sure what ballistics tests from the pros have shown, but I know at close range (from my range time/experiments) the .300 blk hits harder than the 5.56.