To start with, without rhythm, there is no music. Timing is everything to music (just a single tone repeated at an interval can be considered music whereas random sounds do not constitute music). So, number one, the audio system has to maintain a good semblance of rhythm.
Second, for me is the palpability of the sound, primarily mid-range where 90% of the music occurs.
After that, it's your choice also dependent on type of music.