[quote name='king9x']I use HDMI:
http://www.amazon.com/HDMI-1080P-Ou...TF8&colid=1AOQBSAMZWW1N&coliid=I3FSV4RG9LQOD5
Works great for me. (The few times I've used the Wii the past 2 years)

[/QUOTE]
Honestly I'd be skeptical of any device that performs Analog to Digital conversion for under $20 bucks like that, but if it works for you then great. I'd also wonder how much extra lag this would add. Personally I like having the component cable output so I can run the audio leads directly to my stereo to nullify the HDTV lag, which is essential for playing rhythm games or anything with audio cues.
Anyways, back on topic, I have
third party Nyko cables from Amazon I bought for my Wii, and for a good benchmark game like Super Mario Galaxy, it looks perfectly fine on my 47 inch HDTV (good color and contrast, no artifacts). For the PS2,
I used cheap Intec cables, and even with these it was a night and day difference going from composite to component.
I did have to mess around with my TV settings to get the right picture, so I would suggest delving more into your TV's user's manual for more information. For the 360/PS3, it's not much of an issue since the digital HDMI output comes closer to the native resolution of the TV, but for Wii / PS2 you will have to work a bit to find optimal settings.
Another possible scenario is that you have some RF / AC interference nearby that is stronger than usual, so if you can, try unplugging all other inputs to the TV and turn off any nearby electronics (especially any that are running off the same AC outlet plug set). This may be a bit extreme depending on your set up, so you could always try taking your Wii and cables to a friends / family members house and try hooking it up to their HDTV (a whole new set of variables, but you get the idea).