I believe some horn speakers built today have gotten much better at imaging than horn speakers of the past, but if you're a fan of imaging, there are still a lot of horn speakers that don't image real well. I for one am a big fan of imaging and that is why I own Maggie 20.1s. Speaking of Maggies, which in my opinion should always be paired with a sub, can you imagine how little bass they would produce if they were high efficiency? Although there may be some planar speakers that are high efficiency, I can't think of any off the top of my head.
What is your take on high efficient speakers vs. low efficient speakers?
Consider both designs are done right and your other equipment is well matched with the speakers. Do you have any preference when it comes to sound quality? Is it matter of economic decision when it comes to price? - power amps can become very expensive when power goes up, on the other hand large, efficient speakers are expensive as well. Is your decision based on room size? I'd love to hear from you on the subject.