I thought I might give my opinion about the "number one" best speaker.
Well there is no number one. There are a number of "ways to do it"... and I have made a list below.
 Quad Lowther ( or similar) 6" +1" dome tweeter ( most popular)
 RCA LC1a in a world of its own.
Advent with an upgraded crossover. ( let me know if you find a box this size with better bass)
 Planar designs
 Pleated membranes ( Heil)
 Pro driver designs ( P.A.) Horns

Each one of these has "something" that can not be done by the other.
 A lowther big magnet wide range has a peculiar voice quality that is tough to beat.
 Quads are in measurement terms..perfect..; but dynamic range and output are a problem.
 A standard two way 9 6'+1' dome ) are inexpensive, small , but suffer from dynamic range and too much of a load placed on the tweeter in the voice range. ( distortion at higher levels, directivity, and crossover right in the center of the voice range )
 The Advent is a wonderful speaker, needing only a crossover update. It has a unique teeter ( now in vogue in esoteric domes) The woofer has a copper voice coil bobbin to control inductance. The center dome is open .. no unwanted output. ( I suppose if you added a phasor you could extend the upper range of the woofer a bit) The tricky forward mounting of the tweeter-- so the baffle is used to control reflections from side of enclosure. And the odd bi-filer winding of the voice coil..I am not sure why they did this.. (maybe economic?)..... and the bass... Well done Mr. Hoffman.
Planers and Quad all have directivity , distortion at high output ( lack of dynamic range) problems,
Very good acoustic phase, and the ability to reproduce a squarewave. Overlooking the issues. they are very accurate.
 A few overlooked speakers are the .....
Manger, Lincoln Walsh, and keele" CBT line array. ( Audio Artistry ), and Tom Danley.. IMO the best designer today.

As far as horns go.. well it is the best compromise of other systems....
 I refrain from being number one.............. bill