You have a sliding scale of performance when it sounds awful, bad, fair, nice and very nice and this scale is very dependent of the music you are listening to.
Headphones are a rather easy load so it's in other words pretty easy to make a good amp although there are differences. A friend of mine borrowed my QRV04 (OPA627, BUF634), QRV07 (TPA6120) and my masterpiece QRV08 (discrete). All designs have extremely low distortion but the QRV08 was too good. It revealed too much recording flaws according to him but I like to hear everything so it's about personal taste also.