GameCube:GameCube vs Wii

The GameCube outputs much better quality video than the first versions of Wii systems.

Here's some basic GC via original Wii comparisons, both with the official component cables: 

This is due to some factors among revisions and hardware plus software choices by Nintendo:

• The Wii seems to use a 'deflicker' filter when using 480p output, where it should only be used for interlaced output.
• The first revisions of the Wii had a bug in the setup of the AVE chip, resulting in 480p output with incorrect rendering. This is only fixed in Wii models ending in 40 or later. (Wii 480p bug)
• Most Wii games render at 640x480 internally (on NTSC, like the Gamecube) but the screen output is stretched to 720x480 (Rec 601 compliant). Inside this window, games will also account for overscan and can output e.g.: 670x480. The output is 8x oversampled, and it is not a big problem for quality. (Wii-Video Gist)
• GC games will have a different output and Wii games should not fix the aspect ratio to 640x480, as the pixel aspect ratio is not square. Choosing to touch the framebuffer will improve clarity but have incorrect geometry.

For technical information and pictures on GameCube vs. Wii output, please see this thread (and thanks to Sixfortyfive and Artemio for putting all that work in!): Techical Tests, Gamecube vs Wii

The Wii without Gamecube ports is the RVK model and they are pretty much the same as the RVL-CPU-40 and 60, with Gamecube compatibility and 480p bug fixed: Shank's Wii Superthread

Someone recently did a great comparison of Gamecube games played on the GC, Wii and soft-modded Wii U.  If you'd like more details and picture comparisons check it out:  Gamecube vs Wii vs Wii U Video On this comparison, the Wii output is darker, which may be attributed to worn out filtering capacitors. (Wii Dark Video fix)

If you only play one or two GameCube games, than it's probably not worth the time/effort/money hunting down a later edition Wii.  If you're a big GameCube fan, it's definitely worth either getting the official GC component cables, or getting the new GCVideo mod.

Fixes for Video Quality

If you prefer a Wii, the following simple steps can be taken:

• Enable 480p mode and disable the flicker filter (only modded Wii devices).
• Enable the '480p bug fix' in a modded Wii or buy RVL-CPU-40 or later units. (480 bug software fix). Black Wiis exclusively use newer boards and some have GC compatibility.
• Use Nintendon't and USB adapters on models with GC backwards compatibility. Other USB and BT controllers are supported (Nintendont Controllers)
• If the video is dark, replace the video filtering surface mount capacitors, as described in the 'Broken Wii from Japan' Video from MattKC.
• Use component cables and a converter like OSSC, GBS Control or Retrotink.
• Unmodded Wii devices need something like WiiDual to output image comparable to the

Wii2HDMI adapters are of varying quality but will still improve with Deflicker and 480p fix on affected consoles.

Nintendont Performance Improvements

Some people have tested GC games while running on Nintendont. Since this software doesn't downclock the Wii to GC speeds, it has been shown to improve frame rates on some games. It is thus recommend that, on modded consoles, this is used vs official backwards compatibility.