Composite vs RGB, what is the difference?

In playing around with the visual settings on my ntl box, it has an option to be set at composite or rgb, what is the difference, which is better?

RGB will give better quality, but most would likely never notice the difference.  Here a lengthy lesson on it:

http://www.michaeldvd.com.au/Articles/VideoConnectors/VideoConnectors.asp [nofollow]

Thank you very much.

Also of particular significance to UK-Y readership is that when you use composite video you are connecting the video signal fully encoded to the appropriate NTSC or PAL color standard (ditto for S-video). 

When you go down to RGB (or component Y/Pr/Pb) you bypass the NTSC/PAL encoding, and many TVs will then be able to display a picture from the other system even though they cannot with composite video.    It can't be guaranteed, but a large number of modern sets will properly synchronize to the "wrong" scanning frequencies even if not specifically designed to do so. 

More in the Technical issues thread, at reply #34.