There's no universally "best" setting — the right curve depends on the recording and your speakers — but a conservative, general-purpose starting point exists.
Try +3dB at 60Hz, -2dB at 500Hz, +2dB at 2.5kHz, and +2dB at 8kHz. That mild V-shaped curve with a slight mid dip flatters most modern recordings without sounding obviously processed — treat it as a starting point to adjust from, not a fixed answer.
Two people with different headphones, different hearing, and different music taste can reasonably land on very different "best" settings from the same starting curve. Use this as day one, not as a permanent answer.