Let's say you have two folders or slipjoints in front of you. They are both handmade of the exact same materials and are the same design and size. Two different makers, both good. What makes one stand out as stellar and the other not. What do you look for in a truly excellent knife?
If they are the same design, that takes that aspect out of the equation. Same with materials and size. So those don't count.
That leaves my hardest to fill requirement, keeping in mind those caveats.
Fit and finish.
There are a lot of carefully planned folders out there that have been cleverly designed to keep mating surfaces to a minimum. That way you can't tell how much time
wasn't spent in manufacturing, production and quality control.
In the traditional forum, there are a few folder makers that sell their wares there, and their work is superb. The liners and springs look like one piece of metal along the back of the knife. Their scales fit the bolsters to almost perfect tolerances. From the pictures, they don't look real.
I have several production knives like that, but it takes a lot of looking and shopping as well as buying from a trusted vendor.
My last A.G. Russell folder makes me smile every time I see it, and the fit and finish on it are almost perfect. That was a huge surprise; I felt like it was 40 years ago when I saw this one.
So fit and finish for me. I like a knife that shows of the ability of the craftsman to mate surfaces and hold fine tolerances.
Robert