What is your take on high efficient speakers vs. low efficient speakers?

All good comments up to now. I'd only add electrical impedance is critical measure of truly efficient speakers.

As owner and modifier of Klipschorns I have had choice to continue with shallow slope crossovers or go to steep slope. Klipschorns nominal impedance with stock shallow slope crossover rated as 8 ohm, with 104db sensitivity,  it would seem to be easy to drive speaker. In reality there are drops down to 3 and 2.7 ohms with steep phase angles, requires fair amount of current. Taking this into account impacted my choice of amps, 45 and 2a3 SET were considered but eliminated due to these severe phase angles which really require amp capable of delivering some current at 4ohms. I settled on custom built 300B monoblocks which have pretty massive power supplies (each have PS equivalent to what one would normally see in stereo 300B). While I may yet try a 2a3, would have to have pretty special power supplies to cope with these phase angles.

So, for me a truly high efficient speaker is one that 45 or 2a3 flea watt amp can drive comfortably, this would be 100+db sensitivity with benign electrical impedance curve. Klipschorn or other 100+ sensitivity with less benign impedance curve something slightly less than truly high efficient.

To write off all SET in this manner is total nonsense. I've had ss class A and AB, push pull tubes with various power tubes, and SET with various power tubes. Low, medium and hgih sensitivity speakers with the above. So, it seems my evolution towards SET is in fact, a descent into inaccuracy according to mijostyn. I guess having living, breathing performers in room is in fact inaccuracy.