If one can tolerate non-stainless carbon steel, I vote for L-6.
The loggers here in the Northwest use it exclusively in their saws of all sizes because of its toughness, flexibility and edge-holding under hard use.
One could argue that saws don't equate to knives, but these saws look like a bunch of little knives strung along on one piece of parent steel.
L-6 has very small amounts of everything you could throw into a knife steel, including nickel, and excluding tungsten. It has about an 80 year track record.
For stainless, I would choose BG-42.
I have no experience with it except by reputation.
Several highly respected makers use it: Reeve, Loveless and Lightfoot, to name three.
It has the same make-up as ATS-34, except for the addition of vanadium.
A very high tech maker, Timken-Latrobe makes it using the Vacuum Induction Melt and Vacuum Arc Remelt method.
I think this means an extremely clean and pure steel, in regards to unintended contaminants.
Timken-LaTrobe makes this as a stainless bearing steel.
Again, one could argue that ball bearings don't equate to knives.
I have commissioned Gene Osborn of Center Cross Metal Works
(www.centercross.com)
to make a large dagger/short sword for me out of BG-42. Paul Bos will do the heat treatment.
I guess I'll have some hands-on experience sometime in the future, but don't expect any destructive testing.