Unless someone has the exact same monitor as you and the same tastes as you, it'll be near impossible to give you a definite answer for that. Something like that most usually falls into the range of subjectivity. Just play around with the settings until you find something you like, or just leave it at the default values. On my ASUS monitor I personally like the "Scenery" mode, so I use that. If I encounter issues with brightness or contrast in some game, I adjust the brightness and contrast within the game, but not through the monitor. The only thing I can tell you for certain, which should be pretty obvious, is that your resolution and your refresh rate should be at the maximum value allowed by your monitor (i.e. 1920x1080 @ 60Hz).