Another speaker that you might consider is the Classic Audio Reproductions Project T1 or Project T3. The two are very similar, being full range (read: cutoff at 20Hz) and easy to drive all at once. Their efficiency is a little lower then most horns (97db) but they are a uniform impedance- either 8 or 16 ohms depending on options.
I have used these as reference for some time, and while I have heard some speakers that do some things better, I have heard no speaker that does all things better. They are easy to place in the room (mine are 6" from the rear wall, which makes speaker choice difficult in my room).
They are quite revealing and relaxed. Listening all day at any volume level is a treat. I would not put transistor amps on them though! Imaging is excellent and the speaker overall lacks coloration. Its faults: while easily as fast as any cone speaker I have heard, it is not quite as fast as some planar speakers, although for that lack it more then makes up for it by being easy to drive and dynamic, something that all planars lack. If you don't have to strain your tube amp to make it work, your system will sound better.
Finally, the price, which not cheap, is very reasonable compared to some of the lessor speakers listed elsewhere in this thread.
Good Hunting!