high-efficiency loudspeakers

Very happy with Legacy Audio Focus.

I have Zu Druid V’s with a prima luna HP.  Sooooo good!!!

I'm surprised no love on here for the Devore 0/96. I haven't heard them yet but would love to.

Best? There is no such thing. There are too many variables for any absolutes. I'm surprised that nobody has mentioned the Quad ESL 57. There was a recommended 25 wpc maximum on those if I remember correctly. Sure some will like horns, personal preference and all that.
After having many different types and styles I settled on VPMS Tower II many years ago and have never looked back. I picked up a second pair and can drive both pair with a 20 wpc tube amp with glorious results.

Best? There is no best. It's all in what you like.

I had B&W 804s. I thought those were efficient. Then I got the Tekton DI upgrades. Made the 804s sound bad and inefficient in comparison. I now have the Tekton Ulfs. More efficient and even better sounding than the DIs. I think I've slain the speaker dragon. I'm not even looking anymore. Not a very Audiogonish statement, I know.