It seems a really old thread but focus on sharing, MP3, WMA, and M4A are all good audio formats, but I support WAV. MP3 or also know as, MPEG-1 Audio Layer 3, VBR or variable bitrate, is the most common method of mp3 compression, one which I’ve always used from the years 2000 to 2010 when I realised there is something wrong or missing in a mp3 song, especially in the low ends (hi-hats, percussion's etc…)M4A is one of the popular audio formats developed and generalized by Apple. M4A is seldom compatible with devices except for Apple devices. If you want to play audio on devices other than Apple, then you’d better transfer M4A audio to WAV.So, WAV is the best choice. More info about M4A and WAV: http://www.videoconverterfactory.com/tips/m4a-to-wav.html and except these three, FLAC and ALAC are the best formats in terms of sound quality if you have a lot of storage, but they are still compressed and converted.AAC supposed to be the successor of MP3 and apparently, it generally output a better sound quality than an MP3 at the same bite-rate. CD’s have a better sound quality than an MP3 and AAC files. more info:https://en.wikipedia.org/wiki/Advanced_Audio_Coding