No single instrument covers all the parameters that go into good sound, so using just one as a reference is a bad strategy unless that is all you will ever listen to. Human voice ( male and female), acoustic piano, drums, bass, violin and electronic synthesizer would cover it fairly well together.
What Instrument would you listen to?
Ok, this is not the real world, but if you HAD to audition a rig (for purchase) listening to only one acoustic instrument; what instrument would be your lynchpin?
Piano, for me.
Piano, for me.