[gafftaper]

It's hard to say one is better than the other, it's more a matter of which is possible for the type of application you are using.

"RGB" is an additive process and requires multiple light sources (typically Red, Green, and Blue) which are mixed together to make white. However, RGB isn't the only additive combination used. Selador's LED instruments use this technique but actually have 7 different colors mixing to make white.

"CMY" is a subtractive process and uses a single white source. A combination of Cyan, Magenta, and Yellow dichroic filters are moved in front of the light to subtract out colors in order to mix the color you want. (Seachanger adds a fourth "extreme Green" filter to extend the range of colors possible.)