Display mode RGB or YUV - Nvidia Shield

What is the proper Display mode to use for HDTV and movie/streaming use.
The Nvidia Shield Default is RGB 8bit Rec.709. Limited/Full Dynamic range
But does have options for YUV 422 or 444 8 bit.

The display I am using is a LG 32in computer monitor 32MA68HY-P. It is 1080P.

Changing between the modes, YUV seems to be more...dark contrast and vibrant, while RGB is more, normal? I dont know how to describe it.

From what i have read online, Bluerays and other media files are YUV....and its only computer video card output that is RGB. If that is so, then why is streaming box like the Shield defaulted to RGB output.

Channels UI looks much more darker with more contrast in YUV mode. I don't think the display format mode affects the way things are streamed at all though.

Any one with more advanced knowledge on these display formats could chime in and shed some insight into which mode is best?

I have read several things on redit and other sites, its a thing recently with 4K HDR content, but some say RGB is superior, while other say, no YUV is.