FLAC is almost indistinguishable from a 320Kbps encoded MP3 file. The difference, however, is that FLAC truly is loss-less. There is no difference between FLAC and an original CD copy. So if you intend on, for instance, preserving an archive of music, FLAC would be your choice. If you are just casually listening to MP3s, and not creating a library that you will one day re-encode, go with MP3. If you're going to throw out all your CD's and only listen to them on audio devices, use FLAC first. A MP3 encoded at 320Kbps is about half the size of a FLAC file. If you don't care about storage, go with FLAC. There are some examples where you CAN hear the difference between these two, but its very rare. Those differences will be more pronounced on high end audio equipment.