I'm surprised that you are disappointed with the HD output from the PS3!
What size is your TV? Set up correctly, this should look mind-blowing, but obviously it gets better as the screen size gets bigger.
As far as the Wii is concerned, it isn't actually High Def at all.
The component lead will give you 480 progressive output, which is one notch up from the 480 interlaced output that you get from the standard RGB SCART.
If your TV is smaller than say 32", you may be happy with just the RGB SCART, but that costs around the same price anyway, so in your case, I would recommend the component.
Either way, don't just use the composite lead that came with the Wii, as this is a very inferior picture to either the component or RGB SCART.
Hope that helps.
