MP3 320: The most popular choice, great sounding and the highest bit-rate MP3 file which is played in iTunes, Windows Media Player, iPhone & Android phones, etc. Unless you consider yourself an 'audiophile' this is the choice for you. Also commonly referred to as '320 bit rate' or '320k'.
FLAC: (16bit 44.1kHz) Short for Free Lossless Audio Codec, it is a lossless audio format that produces digital audio files that are identical to the original source, i.e. "CD quality". Please note, FLAC is not compatible with iTunes, but is compatible with dozens of other programs.
ALAC: (16bit 44.1kHz) Short for Apple Lossless Audio Codec, it was developed by Apple Inc. for lossless data compression of digital music, just like FLAC above, but especially for playback on iTunes, QuickTime and on Apple iOS devices.