In my opinion, the best survival knife is a sturdy full tang fixed blade. The blade is 4 to 6 inches long. The knife shouldn’t be to wide and must have a sharp point when you want to make a hole or pierce something. The knives I am thinking of are for example the Fallkniven F1, S1, A1. Also the Cold Steel SRK is a fairly cheap and very strong knife. Knives like the Busse, Cold Steel Trailmaster or Becker Brute are of course much better for chopping but they are not well suited for detailed cutting. In optimal circumstances in addition to your knife you should carry a machete in desert or jungle environments and a axe in woodland. In arctic conditions a shovel is of great use.