There is a lot of opinions soundwise so I decided to go for Wav.
This is a ticklish issue, but I think it's important to state the facts plainly. And this is one of the rare occasions where I'm somewhat qualified to speak, as I wrote one of the first popular lossless compressors and also much of the JRiver audio engine.
The simple fact is that lossless compressors sound identical to WAV.
Decoded PCM audio delivery (from an APE, FLAC, WAV, or any other format) happens early in the JRiver audio chain, many seconds before the data is heard and completely detached from playback threads. If the same bits are delivered on the input side (and they are, as this is the whole point of lossless compression) then it doesn't matter the source format.
Lossless compression also provide error detection, space savings, and tagging.
With that said, JRiver has always made it a priority to support as many formats as possible. Each individual user should choose the format they're most comfortable with. JRiver has excellent WAV, AIFF, APE, FLAC, and more support. I consider them all good choices.