NTSC is an analogue television standard, which encompasses all manner of technical criteria such as scan line count, colour encoding, interlacing method etc and in particular vertical refresh rate.
The drop down in your display menu offers 2 x vertical refresh rates; 50Hz and 60Hz. It is not a matter of which one is better, it is more a matter of what media (if any) are you playing.
In its simplest form, you can think of NTSC is 60Hz (USA) and PAL is 50Hz (UK).
If you are simply logged into your desktop doing web browing, photo editing, word processing etc then you may as well select 60Hz. It is the higher refresh rate and so updates will be sent to the screen faster.
However, if you are watching video then you would select 50Hz for anything that is 25fps and 60Hz for anything that is 30fps. (Things get a tad more tricky when you start playing anything that is 23.976fps at which point you need to decide how you perform pulldown). That said, pretty much most media is digital these days, the monitor is full HD and so I assume will play 23.976fps video at 24fps.
So, select a refresh rate and if you see no screen tearing and no judder then you are good to go. Don't lose to much sleep over it.