So what is the best speaker you have ever owned?

Not much of a consensus here?
Just goes to show how different we all are in our tastes and preferences......and also why there are so many different speakers on the market?

Merlin VSM MX. Wonderful imaging,easy to drive,extended highs, surprisingly full bass, and very musical sounding.

Not much concensus, but some darn good speakers in the list. Inevitably, for most people, it is going to be the speaker you have at the moment, otherwise, why did you change it.
I have enjoyed a number of speakers listed above, Harbeth, Proac, Devore fidelity, less so some of the others. For my current set up, with a relatively low powered, Class A hybrid amp, the Daedalus Da-RMa monitors, tick all the boxes. Very fast neutral good imaging, look great etc

Von Schweikert Audio VR-4Jrs. Very musical, good with tubes or solid state. Wide sweet spot. Highs sparkle and lows are solid. Worth more than speakers that cost less, and sounds better than speakers that cost more. In my experience. But to each his own.

K-Horns, Paul was best speaker designer in the world.