The question is "the best for what?" Speaker design, even when money is no object is still a compromise, it is impossible to have the best of everything, period, end of story. There will always be trade-offs in the design.
To use an example, let's say you want a speaker to recreate the dynamics of a drum kit recorded from about 10' away. For those who haven't heard a drum kit from that distance, it is Loud with Huge dynamics, if you had an SPL meter it would almost certainly be swinging off the scale on both ends. If you want to play that back at a realistic level without compressing nor distorting the dynamics, horn speakers are your only choice, nothing else can put that kind of energy into the air without running into trouble.
There is of course no such thing as a free lunch, the price for those dynamics is a lot of stored energy and likely a fair bit of resonance from the horns along with a limited dispersal pattern. The cone of sound emanating from the horn is fairly narrow and the sweetspot is likely to be quite small.
Ok, maybe drums aren't your thing, perhaps you prefer acoustic folk music and you require the midrange of the speakers to be absolutely clear and free from distortions. In other words, no resonances, low energy storage, peaks & dips, or any other funny business in the midrange. That rules out horns and any kind of speaker with a box, leaving ribbons, electrostatics, and to a lesser extent, open baffle dipoles with dynamic drivers as the only choices. This is where the Quad ESL-57 remains the benchmark, that is as long as you keep the volume down. Downsides? Dynamics tend to be limited, they won't play real loud and the bass tends to be on the weak & lean side.
Box speakers as a group, or "monkey coffins" as the late Dr. Gizmo often called them, are plagued with many serious engineering issues. They store a bunch of energy, they resonate all over the place, cause all kinds of diffraction issues, and often have lots of phase, polar response, and time alingnment problems as well. The fact that the best of them can actually make decent music despite all the intrinsic flaws is nothing less than a miracle.
I own a pair of Living Voice OBX-R2s, given my priorities they make the best compromises & trade-offs. They won't play loud and they will run into dynamic compression if I wanted to play those drum tracks I mentioned earlier, but within their limits they're gorgeous.