Which color space to use in camera while shooting video? RGB or YCbCr?
The question is impossible to answer in a general way.

If a camera offers to record in RGB, it is likely using a completely different codec that could be better or worse.  Very few cameras will actually record video in RGB, so if you see the option in a menu, it may be referring to something very particular about the color handling of video on that specific model of camera.

What camera? And what is the exact context of the option?