What speaker has the best tweeter?

The tweeter that sounds the best to your ears is the best tweeter my favorite is the late 40's 16 ohm electrovoice tweeter.

The one that does not give you listening fatigue & the feel that "it's playing too loud".

Plasma tweeters are physically perfect (you can’t reduce the mass applied to excite air any further) but what has been referred as ‘smell a little’ is their production of ozone.
The LD50 of ozone for humans is around 50 ppm, so this is a real concern and this is why they are not made anymore.

I don’t know if one can evaluate a tweeter alone, , in isolation from other drivers in a system.  There are many fine examples, that can work well in the right system, such as Magneplanar ribbons, pleated ribbons (e.g. AMT), and one of my favorites—Western Electric 597 fieldcoil compression tweeters.  The 597 is particularly good at disappearing—you hardly know it is working.  I heard a fantastic version of the 597 made by G.I.P. Laboratories (this tweeter costs $60,000 a pair); it is in the running for best tweeter.

George - looks like you need a 49 ppm quantum tunneling ozone fuse….