What speaker has the best high frequencies?

Tweeters

An AMT tweeter is like a bellows it’s surface area is 3-4 x it total
dispersion area that is why it too has a wave guide .The Spatial use a huge AMT to cover midrange on up ,where others use a specific driver just for midrange which ion a $$ speaker is more costly like a Accuton driver, which also use a diamond particle tweeter which is $$ but very accurate. The spatial is very good 
upgrading or requesting a Xover upgrade will bring Huge results most everyone skimps In capacitors resistors , Path audio best made period but $30 each , vs $3 ,and many upgrade capacitors available. Inductors like a Jantzen great quality,value not too costly 
but many use cheap bobbin type or called sledge hammer coil of 
wire around a magnet 🧲 you see this often in many under $10 k 
just to save under $100. Just for the record when ordering ask to 
have Xover upgrade options  humble homemade Hifi capacitor test gives a very good comparison for modt caps.
Spatial uses a Beyma AMT made in Spain which is very good 
other companies use a smaller AMT just for upper frequencies like Monitor audio for  example Their pl500 can go up to 100 k which is class leading ,even their studio can go to 60 kHz which is like a super tweeter. 

Nola Metro Grand Gold 2. Nola uses a 4 inch ribbon tweeter sourced from Raal. They reach high frequencies like I’ve never heard. Very detailed but never harsh

X3-06 EXOTIC T35

But I have heard them also with a solid copper modified baffle.
SEASExotic-T35Tweeters(CopperFaceplate)

The brass terminals were replaced with copper tubes, and the leads crimped and soldered.

1500-25KHz

There is no one speaker that has the best high frequencies.