Hi Meridius,
Just select the one that sounds best to your ears. Truly. Quite simple.
In your Yamaha manual, they suggest you to experiment.
"Natural" could perhaps be good with Movies.
And "Flat" might be good with Music, maybe.
And "Front" could be more subtle perhaps, you have to listen and decide for yourself, nobody else can do it for you (after all, it's your own set of ears).

And "Through" is OFF, as, sounds best without any of these other Yamaha own EQ curves.
Cheers,
Bob