What's the most important speaker attribute...and

Jayme:

I think that what you have just described is accurate mid-range reproduction, from about 200Hz - 2000Hz. This is the range of frequencies where the human ear is most sensitive and where we have the strongest sense of audio "rightness". If a speaker does not get the mid-range right, the rest is irrelevant.

One of the interesting "fads" right now in high-end audio is the proliferation of speakers with a very recessed mid-range -- and some of these speakers are in the mega-buck category. Some of the high-end audio reviewers seem infatuated with this speaker "sound", whereas several years ago they were raving about speakers that had a very forward, "in-your-face" mid-range quality. A few of the speakers with this recessed mid-range quality also have accentuated high-frequencies that create the initial impression of "air" and "transparency", but after some extended listening you realize that the speaker has poor tonal balance, and it ceases to sound realistic.

Although the audio properties of a speaker are, to some extent, a matter of personal taste, I personally agree 100% with your comment: "If it doesn't sound beautiful, if the instruments and voices aren't naturally seductive---you're not listening to music anymore..."

Since we are all familiar with the TRUE sound of the human voice, it is the best test signal to evaluate the fidelity of a speaker. However, other less accurate speakers may sound better for particular kinds of music. If you listen to rock bands, buy a big boom box like the ones they use on stage. If you listen to dixieland jazz, get a horn midrange/tweeter. I had some very small B&W bookshelf speakers that were great for violin. They were about the same size as the soundbox of a violin. If you must hide the speakers from your wife, get those tiny Bose speakers. If spatial characteristics are most important to you, get some ugly room dividers - sorry..Magneplanars. There is no right answer.

Flat and fast midrange response.

What you said, plus higher efficiency/easy load, plus WAF.

Higher efficiency for flea/fly watt SET/push-pull amps and the rest should be obvious.