More the better.
A simple rule of thumb: when you add up the three numbers the highest sum has the best quality — most of the time.
The three digit ratio specifies the digital sampling structure of HD as well as SD video. Without getting into technical details, VTRs that use 4:4:4 provide the best possible color recording, 4:2:2 is the next one down, 3:1:1 and so forth.
The differences between various sampling structures are invisible to most casual viewers but may come into play in post production when the material is subjected to color correction, keying and compositing.
The ratio does not only apply to VTRs but to any digital device or software that processes video in Y’CrCb (component digital) domain.
Some popular HD VTR formats and their sampling ratios (note that the sampling ratio is not the only factor determining quality of a format):
HDCAM SR 4:4:4
DVCPRO HD 4:2:2