WAVE
From Mario Fan Games Galaxy Wiki
The WAVE file format is a commonly-used sound format that is high quality but has a large file size. Because of its compatibility with many game-making programs, it is used for sound effects in fangames. In the context of games, WAVE is not recommended for music longer than 5-10 seconds due to its file size.
Ogg Vorbis or MP3 are generally better choices for music. If possible, sound effects should use one of these formats as well.