For value I'd argue, unless you're exclusively playing 480i/576i games only, the second best option is Wii Component. For reference here's some screenshots I took which are pseudo relevent to the conversation
RGB through HDMI (Trilogy)
Component through Gamecube (unfortunately stretched by my capture card)
I don't see a strong distinction in colour. I've done other side by side tests but that was before I had my capture card and was with my PAL gamecube and can confirm that, from my point of view (and pretty much a universal opinion until today apparantly) Component cables are far better for games with 480p and virtually indistinguishable without it vs Scart.