The best tweeter is the one that best matches the rest of the system. I've heard a lot of really clean and fast ribbon tweeters that simply did not sound right with the rest of the system. Integration is the key.
Also, the right choice has a lot to do with how much of the frequency range the tweeter is expected to cover. In some applications the tweeter is providing significant output down to 1,000 hz or even lower, in others, the tweeter may be crossed in to provide frequency coverage at MUCH higher frequencies. I don't know about what specific type is inherently better than others, nor can I really take the measure of the sound of a particular tweeter absent consideration of the sound of the rest of the system. I've heard good high frequency sound from systems using all kinds of tweeters.
For most convention box systems, I almost always like the high frequency reproduction of pleated ribbons (AMT-type); they sound clean and seem to integrate well with dynamic woofers in two-way systems. I've heard regular ribbons work well, but, they can sound disconnected and too different in sound with the rest of the system in most applications using dynamic woofers.
The exotic plasma tweeters I've heard in very expensive systems were quite impressive--very clean, clear and open sounding. But, the rest of the system was also quite fast and clear AND VERY EXPENSIVE, so I don't know how they would work in more conventional systems.
As for more conventional dome types, I don't know if I have noticed any particular types standing out as either consistently good or bad. If I had to guess, the majority of the systems I liked had fabric domes.