If I had to pick only one........ anything with a blade long enough and well made enough I could put it all the way through someone! A bonecrusher!!! Id I had to pick only one.
Large blades: a Bagwell bowie, Keating Crossada, or something similar...
Small blades (IOW, something I would actually have with me): Kasper/Polkowski Companion, ShivWorks Disciple, or something from Ken Brock or Mark Goldsworthy
I would probably choose a Strider HS karambit for both utility and SD (I've held one once, but haven't owned one yet ). My EDC rotation is a bit more complex.