"RVZ with the default settings achieves the most optimal balance between compression ratio and playability. Or if you want to save as much space as possible, RVZ with LZMA2 compression at the maximum level.
(just make sure you don't use RVZ with a too big block size, otherwise you'll experience stutters when the game seeks data from the disc -- if unsure, keep the default 128 KB block size)"
The Dolphin team developed a new compression format based on WIA called RVZ. Unlike all the previous formats, RVZ is lossless and can preserve the padding data on Wii discs as well as the necessary files needed by the Wii's IOS. Usage is very similar to GCZ in Dolphin itself, but it only works on newer Dolphin versions.
Archive-quality dump? Yes.
Gain: Immediate (ISO dump size lowers). Considerable, depending on the game.