Is the most efficient speaker the best speaker?

You guys are missing some key points. All speaker designers want to have high efficiency but you can't always get it without compromising something else, like frequency response or a changing impedance. As in most engineering, you have to make choices and it's up to the designer to make the changes he/she wants, efficiency is one of the first to get compromised.

Prove it.

You know guys, it seems to me that the op really just wanted to know if if efficiency is something to seek out.
We have all blown this up. I have built speakers from 84 db sensitivity to 99 db sensitivity... The all sounded quite good in their own right. In my experience, there is no requirement of high sensitivity to make really fine sounding speaker, nor do really high or low sensitivity speakers sound one better than the other. They do have different requirements for power and placement and what type of amp that they sound best with.....
The good news is that the ops question as written is truly impossible.

Efficiency in of itself is a good thing.

But alone, efficiency means nothing except volume.

I think we can all agree there is more to it than just that?

Atmsphere, of course that is only your opinion, many if not most, have come to the opposite conclusion.

Sorry, Unsound. What I have stated is simple fact; its not a matter of debate nor can I do anything to change it. Facts are like that. If you seriously think that what I stated my opinion then I advise you to study the theory and history of audio.

Now it is true that the majority of the audio industry has chosen to use the Voltage Paradigm. If you look at history you will see why- high efficiency speakers are more expensive to build. Just follow the money.