I have heard quite a few high efficiency speakers. All of them have trade-offs which you may or may not find important, depending on your preference for sound.
- Large horn speakers (e.g. Avantgarde Duo, Trio, or Acapella): the most explosive dynamics and able to fill the room with sound. However, more often than not the horns do not integrate properly and imaging is very poor. Needs a large room and budget.
- Dual Concentric (e.g. Tannoy). I have heard quite a few of these, and nearly all of them have natural lifelike dynamics (horns can sound a little excessive), wonderful coherency, and superb imaging. The downside is the rosy coloration or a midrange thickness that makes everything sound rather 1950's. The other downside is that they should not be played too loud, otherwise you may damage the speaker.
- Full range single driver (e.g. Coral). I have not heard a single one of these speakers which I like - rolled off top and bottom, and they sound small and incapable of filling a room with sound (unless you have a small room).
- Boxed multi-driver (e.g. Zu and WLM). These tend to vary quite a lot and do not have a sonic signature which can be generalized to the whole class of speaker. I find most boxed speakers to be fairly boring in sound and it's difficult for me to get excited about these.