How do you know a loudspeaker is the best?

Marakanetz, as a musician, the instrument always sounds much different when you playing it as a musician than when you are listening to it as an audience member. The vantage point is greatly different and some of the sound is likely being inducted through your body and bones.

It's sort of the like the descrepency you notice between yourself speaking and a recording of yourself speaking - although that is an extreme example.

Adding to Aroc's comments, when the instruments start sounding the same as you described in your step3 Marakanetz, it is more likely that you've become a good player of many instruments than having the best speakers.

Listen to really high end speakers so you know what's possible -- then, try to get as much of that; Coherence, natural detail, resolution, sound staging, air, extension, tight bass, musical, etc. as you can at the price range in which you're shopping.

After years of saving, I finally have accumulated enough to buy some top-rate speakers. For the last year, I have been going from dealer to dealer auditioning speakers. I started off with some B & W 705s. Something was missing. Went to another dealer and listened to the B & W 805s & 802s. Better sound, but I still wasn't satisfied. Went to NYC several times. Heard the Revel, Dynaudio,Vandersteen 5A, and Wilson WATT 7. Still wasn't hearing everything I was anctipating. Then I heard the B & W 800s. And all of a sudden I heard everything I wanted to hear in a speaker. (By the way I kept bringing the same CD's to the auditions).
I share this with you not to sell you on the B & W s; but to inform you of the process I went through to find speakers that worked for me.
As some of the other correspondents suggested, keep listening until you find the speakers that work for you.

Your question suggests that you have no basis for evaluating the quality of a speaker. The only thing I can assure you of you don't measure it by its cost, size or type. Design and quality of parts/built are very important but they don't make a speaker "great" either.

If I were to assume that you already had the best electronis and sources, then I would say the speaker that is "best" is the one that sounds best to you in your room. That is YOUR great speaker. But if you don't have the best room, or the best components, that same speaker may produce sounds that lead you to believe it is a POS or some such negative evaluation, but another speaker may work just fine with the same stuff (this indicates a probable mismatch between the speaker and you room and/or electronics.

It's really about your room, your expectations, your finances.