Depends on your room, speakers being used, size of sub woofer, amp set up ect.
There is no "best setting" for every application. If that was the case a variable control would not be needed.
Some rooms are boomy, which would lead you to turn down low freq's. Some rooms are very splashy, in which case high will need to come come down. Some rooms are very dead in either lows or highs, in which case those freq's would need to be increased.
To get a baseline on what your rooom is like send some pink noise through your system and analyze it with a RTA. (real Time Analizer) There are free apps you can use on your phone or pro audio products that do a very good job. With pink noise being pushed through the system you will see what freqencies are naturally louder or softer in your room. Then you can adjust that real time on your eq and see the changes.
This will set your room to a flat response, however lots of people don't like that sound and want more punch,growl, or clarity. In that case simply adjust the low, mids or highs to your own listening preference
If you need further help, I’m available over the phone at https://www.6ya.com/expert/gregg_27a4d257e54e7920