Define "valuable".
Colored X1s cost money. The others cost experience. What's more "valuable" to you? I piled up 20m credits in not too much time by doing B-spec grinding while I was at work or asleep, and eventually got to B-spec L40, so I can buy the colored X1s now. But I still have only the one that I *won* (for hitting L35). So which is more valuable now? The one I spent every last penny on, or the one I spent a whole lot of time on?
Since I haven't won the CF one, and you can't buy it at the dealership, maybe that's the "most valuable" one. But I could trade for it, easily. As I could any of the others.
"Value", in this game, has no meaning at all.