Well, since size of the tweeter is your criterion, then the "best" would be the three panels in the Kingsound King III electrostatic speaker, of course. (reviewed for Dagogo.com)
What speaker has the best high frequencies?
I have a Spatial Audio X5 with a wide band horn loaded AMT (Air Motion Transformer) which handles high frequencies (1k and up?). It is big, about 6” x 1”. I feel it is much better than the 1” tweeter found in most speakers. I honestly don’t know how this AMT is different from, say, ribbon tweeter. This leads me to think, who or what speaker has the best high frequencies? I heard good things about the B&W diamond tweeter, but it is still a 1” tweeter. What else is out there? I think size makes a difference. In this case, is it a larger ribbing tweeter better than most 1” tweeters?