Getting back to the original question here about being stuck deep in the field somewhere, I would go with a good sturdy fixed blade with a sturdy sheath and a blade between 4-6 inches. Doesn't have to be fancy.
Folding knives can break and are harder to clean. A basic fixed blade can be fasioned into a spear for fishing, or for defence against a preditor.
Almost 9 pages and someone finally said it.
A fixed blade between 4-6 inches is about as versatile and durable of a tool as I can think of, especially if I can have only one such tool. Plus, in a survival scenario, you have a chance of the thing actually being on you. Doug Ritter points out, for example, that large knives are really nice and useful, but when you get to climbing into boats and small aircraft, you'll probably put that big chopper in a bag or something, while the 4-6 inch belt knife has a real chance of actually being on your belt.
I assume that I don't get to pick in advance the tools that I'll have in a survival scenario. I can only carry what I would naturally carry and hope that if a survival scenario comes to me, I'll have what I need to survive.
What I'm saying is, if you assume a downed aircraft in the far north on a, say, fishing expedition, chances are I'll have a decent PSK on my belt, a 4 - 6 inch fixed blade on my hip, a neck knife/compass/whistle/small firestarter around my neck, and a folder in my pocket. Heck, I might even have a leatherman in there somewhere.
In a bag somewhere, I'll have a big chopper and/or an axe. Do I get to retrieve said bag from the downed aircraft after the event?

How about the siltarp, tent, sleeping bag and other camping equipment that's also in that bag?
These scenarios would be a lot better if someone could explain to me how I got into the situation in the first place.
