What speaker has the best tweeter?

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.

<<<Don’t know where you get that idea, these are the newest horn loaded ones, but are little colored sounding because, of the horn and don't have a 360 degree radiating pattern
https://www.lansche-audio.com/products/plasmatweeter/

Cheers George>>>

Searched a little for web links, but this was late 70's/early 80's and all I can find is in German. I lived in Cologne at this time and actually visited the Magnat factory. Learned there that the main function of the wire mesh sphere was to lower ozone emission by establishing a steeper temperature gradient. But the smell was quite obvious and the claim 'below legal limits' applied to a pretty short listening session (30 min I believe) and a ventilated room. Easy to see how this leads to issues in the real world. Magnat discontinued the tweeter although it earned the brand recognition, even admiration as a serious innovator.
The press was simply to negative ("Ozonschleuder", something like "ozone pump"); people didn't want them around their kids anymore, and cases of headache/nausea were reported.

Later, companies like Plasmatronics used Helium to minimize ozone emissions. The Corona design also successfully suppressed ozone.
But Magnat never went back.