For true survival situations an Americanized tanto will be useless unless you're a mall ninja survivalist. You may as well carry a putty knife or a chisel. Stick to tried and true traditional designs that are adept at multiple tasks. A blade length of 3 1/2"- 4", and most importantly a solid lock-up. Go with a custom if you're really serious, heat treatment is crap on store bought cheapo knives. Proper heat treat will insure toughness and good edge retention...it's the heart of the knife. That being said, think of a folder as a back up, in a survival situation you can't beat a custom sheath knife with a 5"-7" blade. If you think about it, survival won't be trying to impress people with your knife...it's about helping you stay alive.

Yes, I'm biased....I make customs.