We probably all hear things different and have our audio equipment positioned in different listening environments, some rooms may have, padded furniture, carpets and curtains and similar sound absorbing materials in the room, whilst others may have hard reflective surfaces like tiled floors… so the best EQ settings are what actually suit your own room and the way you like to hear the audio when sat in your chosen position to watch/listen to your Audio/Video sources, which too may change, depending on the codec used and how the original source was recorded and engineered. 

You just need to first Trueplay tune the room with an iOS controller device and then adjust the EQ settings to best suit you and your own environment.

You can read more about Trueplay tuning the Sonos devices in your chosen room here in these links:

https://tech-blog.sonos.com/posts/trueplay-spectral-correction/

https://support.sonos.com/s/article/3251