Wii U to Switch by far. GameCube wasn't exactly a failure, it really just followed the downward trajectory we saw from the NES to SNES to N64. The Wii was a huge success saleswise, but became a shovelware dumping ground in it's second half. This was a big reason for the Wii U utterly failing, together with it not really offering anything new (except for a second screen nobody wanted). So the Wii, while very successful, didn't bring further success. It didn't make people want to buy the next one, and that almost killed Nintendo.
The Switch was an incredibly successful new concept (even though it was really just the Wii U idea executed much better), and it never devolved into the trash the Wii was at the end. The Switch 2 now keeps riding that wave, and while I don't think it will sell as much as the previous console, it will be a success. People want the new Switch, they didn't want the new Wii.