Which is better ycbcr or s video connection?

YCbCr is more commonly known as component video and uses three signals. The first carries "luma" or brightness information. The other two carry color information as difference signals. The format carries full image information.

S-video uses two signals. The luma signal is the same as component but the color information is encoded from two separate signals into one. The result is that color information is lost and therefore S-video is inferior to component. The difference is quality is not great so S-video delivers a perfectly acceptable image and is also significantly improved against composite signals.