You know, this topic reminds me of a little test I did last year.
On another forum we were talking about the popularity of the flintlock over the caplock, and how/why the flintlocks held on in popularity (which is still true to this day) that if you ran out of caps for your rifle - well, you were just plain screwed until you could get somewhere to get those percussion caps... However, if you had a flintlock rifle and you needed a flint for it, you could pretty much find something on the ground (flint or chert) that you could fashion into a flint for your rifle.
So I decided to do a little test last summer and found what looked like a piece of chert on the ground, picked it up, took it home and fashioned it as best I could into a workable flint that would fit the jaws of my lock and gave it a try - by golly it worked! It pretty much put the above mentioned topic we were discussing in prospective.
Now this post has nothing to do with "Best Flints" but it does shed light on the subject that a flint (no matter who made it or where it came from) as long as it works, it's a good flint.