What speaker has the best tweeter?

I used to use a Tannoy super tweeter with my Tannoy Westminster Royals. Even though the st’s frequencies were far beyond my hearing, the st had a significant effect on the lower frequencies.
Think the nodal points became more pronounced.

My Vandersteen Treo CT’s with carbon tweeters are the best I’ve heard.  

I guess a lot of people have not heard big Mageplanars. The ribbon tweeter in the 20.7 is handily the best tweeter made and I do not expect that to change soon. It does everything right. It is effortlessly smooth and disperses perfectly. As a line source dipole it limits room interaction and will sound great in just about any room you put it in. The only downside is it can be a bit fragile but Magneplanar has an excellent tweeter replacement program. They will have a new tweeter to you in three days. You put the old tweeter in the shipping tube the new one came in, apply the return shipping label they give you and they will refund the core charge when the get it back. The magnet structure is immortal, they just keep rebuilding them. 

The DMD tweeter in my Usher Dancers is pretty darn good!

All of my designs have made the tweeter sound like the best one.  It's ALL about the design and the crossover, using the right tweeter in a given design.

That said, there are dogs, but most soft dome tweeters and decent ceramic tweeters can be tamed into very good performers.