it is going to be different depending on what your room is like, when your optimal times for viewing are (when the best picture is important to you), mainly what time of day/how much light is in the room.
there should be default settings to make it brighter at the touch of a button but then switch right back to saved user settings. my reccomendation is to set the tv in the lowest ambient light possible (night) and adjust it to what looks best to you…simple as that. online reccomendations will get you so far but every person is different so…
good luck. its all about the mirrors