If the end of time is near (and I can only have one gun) I'd pick my American Arms Turkey Special 12 bore. Built like a tank and will digest 2.5, 2.75, 3.0, and 3.5. Steel, lead, tungsten, buckshot, slug, etc. etc.

However, if I'm just so broke I can only afford one gun, then I'll take my Parker DHE 20 and a flat of RST's. (smile)