Wow. Great thread idea. No one's ever thought of this before.
In my humble opinion, it would be one of the carbon steels. U.S. Schrade's carbon (1095, IIRC) is very good, Camillus' 0170-6 (Carbon V) is very good, and Case's CV is great stuff too. One of the best values on the market today is the carbon steel Mora's.
There's Canal Street's D2, and GEC's carbon steels, neither of which I've used much.
The same old adage applies: it depends on what you'll be using the knife for, how hard you'll be using it, etc. For me, cost and edge holding have to have a happy medium. An expensive knife that won't hold an edge isn't worth anything, and a cheap knife that keeps it's edge but is too difficult to sharpen . . . isn't worth much either.
There are a number of 'super steels' out there that will hold an edge for what seems to be forever, but they are can be a cast iron b!tch to sharpen. ZDP-189 is one example. (I know from experience with that one.)
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