Voicing is the adjustment of a piano's tone or quality of sound. Tone can be changed without affecting the pitch. For example, turning the bass or treble knobs on your stereo changes the tone but does not alter the notes the musician recorded. A skilled piano technician can voice a piano to change its tonal personality from mellow to bright or robust to delicate. The degree of change possible depends upon the piano's design and condition.
Tone varies, even among pianos of the same make and model.
No matter what its size or cost, any good piano should provide a wide range of tone, from soft and sweet to loud and bright. The tone should be even from the lowest to the highest notes. Most of all, it should sound musical. There is no single answer, because everyone's taste varies. Also, certain tonal characteristics are more suited to specific styles of music.