Separate names with a comma.
Not really, they both have their advantages and disadvantages and are meant for different purposes
Even though Extrasklep is right, I'll have to take the side of "flac is better". Even the old3DS can (although barely) keep up with 24bit192kHz flac decoding. FLAC is basically compressed wav, there are very little reasons to NOT use it.
Slighly off-topic but I'm curious, can the 3DS actually output at 24bit192kHz?
The CODEC has two known I2S output modes: either 16bit ~32728.49Hz, or 16bit (or perhaps 11bit?) ~47605Hz.