Its a toss for me either the BPS 3" 12ga or the 50s vintage Winchester model 12.
Then there's the 1903-A3 or the 48-22 Yugo Mauser.
My Blackhawk in 45 Colts. Lot of faith in my Hi-Power clone too.
If you meant end of the world like then its gotta be the Marlin 1894 and the Security Six only because I don't have the other Mauser bbl'd for 460 S&W/410/45 Colts to go with the BlackHawk.