There are good and bad examples of all kinds of speakers with different attributes. Assuming the speaker has a reasonably smooth and balanced frequency response, the efficient speaker has several particularly important advantages. The primary advantage is that, at least for my taste, the very best amps are low in power output. I like tube amps, but, mostly those that do not use higher powered pentode output tubes that are used in large quantities to achieve high power, and even solid state amps seem to be better sounding if they are not extremely powerful (e.g., First Watt amplifiers).
The other advantage is that high efficiency speakers tend to have better dynamics because they will deliver decent volume without as much power being dissipated as heat. That heat being dissipated in low-efficiency speakers increases the resistance of the electrical component, which means less current/power can be delivered; this is thermal compression that means the volume level does not increase in proper proportion to the signal level.
