I don't have enough time or money to actually know what the greatest folder out there is.
What I do know is this-
A $70 Spyderco Endura is the perfect 4" folder for me. If you want smaller, the Delica is the same knife but reduced in size by 30% or so. On a budget ($25), I've been pretty impressed by Byrd (cheap Spyderco) and spring assisted Kershaw 'Speedsafe' models.