What is your favorite type of tweeter?

Plasma tweeters. Nothing else comes close. The first time you hear these, you will be astonished by how slow everything else sounds. The sound emerges from space, as if from nowhere.

My pet hates are metal dome tweeters. All of them sound metallic and harsh. Particularly bad when partnered with solid state amps.

Amfibius,I have to admit I've been fascinated with the concept of those Plasma designs.

The Lansche speakers look to be amazing,in that they have a unique bass augmentation,coupled to a superb mid,and the Plasma tweet!!All,in a somewhat small package.

Though I've not heard a plasma designed tweeter(actually,I may have heard the earliest type many years ago,but don't have a good fixation on it)I can see no technical reason to doubt your input.Except....

There are some darn good metal dome designs,which need good matching componentry.Otherwise the gag impulse sets in quickly!

Still,the Plasma design should be magnificent!

Best

I second the Essotar tweeters in the Old Sonus Extrema's and The expensive Dynaudio's. Those and the inverted one's in the Wilson's and JM Lab's Eutopias are veryy good. But I'd have to say I like the Essotar's for dome's, best overall (however hard to drive)

Thanks to all for the great comments.

The Gallo CDT was mentioned by several people. I have not heard this speaker or tweeter, but will make a point to do so.

Ribbons -- love the ultra-low moving mass compared to domes, but don't love the distortion, the fragility, the limited vertical dispersion (especially for the taller ribbons) or the high crossover requirements. To go lower with a ribbon, you need a taller, heavier ribbon, so vertical dispersion gets even worse, and you sacrifice the moving mass advantage.

Fostex horns (T500mkII and others) -- these are supertweeters, and can't be crossed low enough to be used as regular tweeters.

Plasma (ion) tweeter -- I listened to this tweeter on the Acapella High Violin 2 years ago. It was certainly a very sweet, smooth, pleasing treble, but there were occasional crackling noises as particles of airborne dust got zapped in the plasma discharge. There was also a faint baseline hiss from the plasma discharge, amplified by the horn, audible within 12 inches of the tweeter. Overall, I am not certain this tweeter would consistently win a blinded A-B comparison against a top quality dome or ribbon. Due to the very high cost and electronic complexity of this tweeter, I cannot justify it, especially when there are so many less-expensive, simpler and more reliable, great-sounding designs out there.

But now I return to my original question: if you were designing a speaker at the $5K or $10K price point, would you go with a dome or a non-dome tweeter? Since domes are the dominant tweeter technology in that price range, is it better, businesswise, to stick with a known, familiar technology, or is it better to set oneself apart from the competition by using a non-dome?

It depends on what you are trying to build.Especially the bandwidth of the midrange driver.Do you design similarly to the Scaena,with minimal crossovers or use steep filters and phase compensation.Many variables.
My first thought would be the midrange driver,its' bandwidth /effiency.With the proper choice,the tweeter is more easily integrated and need not carry a heavy load.IMHO.