Is the most efficient speaker the best speaker?

Unsound,
High efficiency speakers may(or may not) be more difficult to implement sucessfully, but fortunately there are enough of them available that it`s a viable option for many. They sure work for me.

I'm glad they work for you.

All other things are never equal so its a useless question unfortunately.

More efficient speakers are more efficient and that's about all you can say about that.

Most portable electronics that operate out of necessity on low power are very efficient. DO they all sound good?

case closed.

Touche'!
Some times one can use the basis of "all other things being equal", but I don't think it works at all for loudspeakers, not for the time being anyway.

All the speakers that I have owned and liked best have been sealed and they are less efficient than most others. To my ears a sealed woofer gives the best bass of all other designs.