I have some popular knives like the BK-15, ESEE-4, and Mora, but lately have also been exploring the utility of the extreme low end of the spectrum. I think a few really cheap, junk, knives could provide a good baseline for performance expectations and comparisons (for me). They're also good fodder for practicing grinding and mods.
My latest pickup just arrived yesterday, at literally $8.13 to my door, the MU-1130 (MTech-kin, lol):
Roughly similar to an ESEE-4 in overall length, stock thickness, blade shape, etc...