Too many variables to say if one is better than the other.
Depends on source, display etc. etc.
For example a dvd is stored in component on the disc, 4:2:2 YCrCb component to be exact, so idealy you take it out SDI (as this is what SDI uses) so there is one less A/D conversion being done and also one less D/A conversion being done. Then put that into the scaler and then output whatever the screen prefers, some screens will take RGB straight in so RGB is prefered, others convert to component so you can have total control of colour and tint etc. if that is the case then going in YUV may be preferable as it will not have to be converted by the screen on the way in, the screen will convert back to RGB on the wat to teh display though.
So unless you get the specs for every piece of equipment you own and work out where conversions are done and then try and set it up with the least conversions going on as possible I would not worry about it!
Having said that changing colourspace is always done pretty well these days.