A lot of this boils down to personal preference, but there are a few factors that can make one sheath better than others. A sheath’s draw for instance is how easily the blade can be pulled from the sheath. There needs to be a good balance of hold and give for the knife to function properly.
A sheath’s latch can be problematic if it snaps too hard and is difficult to open. Survival knives should be easily accessible in case they are needed on short notice.