I have both 500 and 870, the 870 is tactical model w/ghost sights, nice. The 500 is the plastic stock set w/pistol grip, matte finish. I added houge pistol grip set, very nice shooting with the pistol grip even one handed. I recommend both guns, mine both of 300+ 12g rounds down the tube.
The 870 is a beast with the steel receiver. The 500 is lighter, and has double extractors. The bonus with the 870 is a loader gate ramp, to keep shells from falling out of the bottom which I had once or twice in my 500.
You can't go wrong with either, they been making guns for years. I would just flip a coin if I had to do it again. Really enjoy both of mine.
SHTF vs TEOTWAWKI you ask? SHTF, just some crap on the ceiling and walls, TEOTWAWKI end of the world as we know it. Orignally made by 9mm/®™©