It varies in what you want.
If you want something sharp and cleaner for capture, or a good scaler (an individual one or a TV with a good one), evWii with the 720x480 and 720x576 option outputting 480p and 576p may be the better for that with the Wii U Wii mode.
With a bad upscaler or using the default output from Nintendo's firmware (or also wanting a bit softer but not too much scale), 720p and 1080p may be better. The scale isn't perfect, but for most it should be fine.
If wanting an overly softer image, using the 480p output with the default Nintendo firmware and settings I guess, if someone wants that for some reason.
The problems with the GamePad isn't only about the chroma shift, but also interpreting the colors as the wrong color space, which it's also something that may happen on some TV's and devices using HDMI, since the Wii U doesn't handles it properly to what the display should use (it's outputting 601 as is without converting to the GamePad color space). This is easy to notice on reds.
There's also the option of a real Wii of course, and apart from not having all the drawbacks of the Wii U's Wii mode, it's also probably the best for CRT TVs, the Wii U does something a little weird with the interlaced output and it won't output 240p. But it's analog video only unless one mods it.