(How'd I miss this thread.)
Nowadays, it'll be subjective since there's so many equally good choices for whatever you want it for.
To me, you can't really go wrong with the Spyderco Delica, Endela or Endura (smallest to largest). The Salt 2 and Pacific Salt 2 are your Delica and Endura in highly stainless steels for saltwater environments. Classic lockbacks, so, simple to open and close. Good ergonomics. Both left and right-handed. One-handed opening. Rugged (beaten on a Delica and Endura beyond what you'd use such for and they held up fine). Lots of choices: steels, scale/spacer colors, blade geometries, grinds, and edges. Aftermarket scales, screws, and so on. Outside of the fully serrated Endura, they look friendly enough for civilization. Good for utility, outdoors, indoors, work, and if there's nothing else, fighting. The basic VG-10 models might be a little pricey, but they should last a lifetime. If I had just one knife, it'd be an Endura of some make.
My favorite folder is the Spyderco Military, but they're kinda stupid expensive nowadays, at least where I live (I got my basic S30V version several years back when they were about 1/2 of what they are now). I don't really use it.
(Not a Spyderco fanboy, rather just those examples I like.)