The way a speaker sounds ...
Given everyone has their own preference, I prefer speakers which are fairly neutral. I like to have a system with the characteristic of getting out of the way of the music so as I listen I can have a sense I am there during the performance. Words such as transparency, clarity, soundstage, openness come to mind.
People have differing tastes. Some like a booming bottom end, other a precise high end, etc. Get to know your own preferences and find favorite source material you love, which you know very well, and can use to listen to various speakers. That is the best way to assess a speaker's sound within the context of your preference.
Best,
Mike