Well spoken rotte. I like to think of it as different strokes for different folks.
A lot of people have orient there choice towards bugging out away from the cities to the forests or woods. That is a knife selected towards fire making, skinning, wood work, chopping and food preparation. Perhaps a medium (bk2, sfno, skinny ash) to larger (golok, machete, nmfbm, fbm)
But to put a different spin on things has anyone looked at the scenario where the SHTF, something other than zombie attack or total power black out with city street riots, to something that is more likely to happen (and seem to be happening more lately) like major storm damage (hurrican Katrina), wide area flooding, earthquakes and now large bush fires or wildfires?
I really like the medium sized blades like the cg ash1 where its short enough to be carried and strong enough to pry with and maybe even a bushwacker BM since its lighter but what if you were trapped in an urban situation and had to break through a brick wall or rescue someone in a building?
I guess you could use the two just mentioned but it would probably be hard work. What would come in real handy would be the back of a solid axe to smash bricks. As someone has already pointed out, an axe can be choke gripped up by the head for fine cutting or skinning. Not as good as a rat rc4 but would work fine.
I know that a single blade can't do everything and there are some choices from others that can just about do it all. But in a real situation maybe a single blade is unrealistic. Like others I would like two or more. A small and a big (like a skinny ash and a machete).
But following the original question in that if only you had time to grab one if the SHTF scenario then it would probably be a mid to largish (6" to 8") A cg ash1 to maybe a nmsfno or sar8. Personally any mid to largish would do the job either it be a busse, cold steel, rat, kabar, becker or even a mora.
In an emergency situation you might not even have the time or choice to get what you really want and only the time to grab anything. I like to think that what ever you do grab I would still like to have a sharp mind. Learn how to use any blade of any size or shape. Your skills will be the most important choice you can have and practice practice practice.
Someone quoted Bruce Lee once in this forum and I think it holds true. 'It is not enough to know, you must do.'