It would not be difficult for me at all. It would be impossible.

And that is without asking for your definition of "best". lol
Having just started collecting knives in the last couple of years, virtually all of my best knives are
1. new
2. unused
3. Probably going to stay that way for quit some time.
In the past, I thought $50 was the most anyone should have to spend for a really good knife. As most of us have experienced at one point of another, the amount we are willing to spend on a knife goes up, the deeper you get into the hobby.

So that being said, my best, and most expensive knives are - for the foreseeable future - nothing but safe queens and I am fine with that.
Depending on what your meaning of "best" is there are different candidates.
Sharpest - is a Santuko knife from Japan that was given to my uncle by a client of his. The damned thing could have sliced a razor blade right down along its edge. Have no idea what the brand was.
Best of Purpose - Fine detailed cutting. An Exacto knife can do what nothing else can. Fileting fish, got 3 that fill the bill, all just different sizes and perfect for the task.
But for my money, of my user knives, the winner probably goes to a knife, sold under the Cabelas label back in the mid to late 80's. I didn't even know it was actually a Boker until just a couple of years ago when the company confirmed it. It was made in Solengen Germany so this is not the cheaper Arbolito, Magnum, or Boker Plus, foreign produced lines of Boker. Classis drop point hunting knife with bone scales. Love it. If I put it on the market, it would probably sell for more than any of my other knives at this point, but not interested. Will keep it and hopefully put it to use on a few more deer in the future. Maybe even an elk, moose or a caribou if the lotto people would stop playing favorites and pull my number for a change.