CD ripping

M4a is a lossy compression format and inferior to the wav format. But wav files don’t accommodate meta data. If you’re going to rip your files again, it would probably be best to use a file type that has no loss - such as flac - but that can also include meta data.

Absolutely, in my opinion you should re-rip your music in either .wav or .aiff formats.  The foundation of your digital library should be uncompressed, or at least flac, for the best sound quality.  Once you have them ripped to uncompressed then you can play with your files and compress them for portable playback, for example. And make sure you have files backed up properly. Db poweramp or XLD are terrific programs for ripping. 

Wav or uncompressed flac.  

I agree with andrei nz.  Personally, when I compared WAV vs ALAC ripped files, I could hear no difference.  Not sure about the correctness of cleeds comments w/respect to M4a from ALAC.   ALAC compresses but is claimed to be lossless, as in "Apple LOSSLESS Audio Codec".   Regardless of any theoretical advantage for one format vs the other, let your ears be the judge.  Re-ripping would be a lot of work not to mention losing meta data with WAV.