That will be subjective to you. Instead of changing modes, I simply find one mode that works for both games and everyday work. On my monitor, I use Multimedia and Adobe RGB all of the time.
* Open the U2415 Menu OSD (On Screen Display)
* Go to Others
* Choose Factory Reset- Reset all Settings (This will set Brightness and Contrast to 75)
* Go back to Color
* Choose;
Input Color Format = RGB
Gamma = PC
* For Preset Modes =

- Standard: Loads the monitor's default color settings. This is the
default preset mode.
- Multimedia: Loads color settings ideal for multimedia applications.
- Movie: Loads color settings ideal for movies.
- Game: Loads color settings ideal for most gaming applications.
- Paper: Loads brightness and sharpness settings ideal for viewing
text. Blend the text background to simulate paper media without
affecting color images. Applies to RGB input format only.
- Color Temp.: Allows users to select the color temperature: 5000K,
5700K, 6500K, 7500K, 9300K and 10000K

* Test each one in both games everyday work. Find the best single one that works for both. Then you can tweak the Brightness in the video card control panel