What speaker has the best tweeter?

No such thing as best, each design is unique.
in a AMT tweeter the Beyma is probably the best .
Accuton has the great $2k Diamond ceramic tweeters ,
Plasma tweeters are very unique and great ,but need to be recharged every4-5 years ,MBL 101 Omni directional speaker 
great in that application , then custom dome tweeters  that have their own attributes several very good brands ,
and some very good Ribbon tweeters . That’s my opinion .

Multiple tweeters unless of very high quality, and matched to within 1db and be $1-200+ each then  they are subject to multiples of HF distortion ,that is why 
you don’t see them in any high end designs ,or very rare.

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.