Is the most efficient speaker the best speaker?

To the OP's question as stated: yes.

To my ears, only high-sensitivity systems really "breathe" and allow the use of low-powered, more refined amplification without compromise. Low-sensitivity speaks sound as if a wet blanket has been draped over them, comparatively speaking (ahem).

But, to each his own.

Triode needs to hear better non-flea tube amp powered systems.
They do exist!

I also like SET amps and high efficiency speakers as they can sound quite good also.

"But,to each his own"
Triode , words of wisdom. The low power amp/high efficiency combination seems to more sucesfully present the flesh and blood, living breathing presence that`s so convincing. This ability to consistently create such realism is what pull me over to this genre.(is it the much simpler circuits and fewer parts?). Trumpets,pianos,saxaphones and human voice is simply much closer to what I hear at live performances, the palpable reproduction is stunning at times. YMMV.

These kind of discussions would have more weight if we were to quantify what is high sensitvity, medium and low ..

A horn speaker with a sensitivity of 100db/w/m being driven by a 20w SET, will have far less db gain and dynamics when compared to a planer speaker with a sensitivity of 86db/w/m being driven by a 200 watt amp @ a listening distance of 15 ft.

regards,

Hi,
Weseixas, basd on your example of the two systems above, the horn/SET 20watt wouuld have much more available headroom (dynamic reserve)than the inefficient system. At 15 feet(roughly 5 meters) to achieve a sound level of 94db the horn/SET would require 4 watts, the planer/200 w system would need 128 watts. 5 divided by 20 is a much smaller % of available power rhan 128/200w, thus far more reserve headroom for the higher efficiency system.
Best Regards,