Audio File Formats
MP3 is the most widely-supported audio file format. If you’re not sure which format to get, it’s the safest bet. My MP3 are encoded at the highest available rate, 320kbps.
AAC files have better sound quality than MP3s. They work in iTunes (both Windows and Mac), and should work with most modern mobile devices. AAC is the format sold at the iTunes Store for downloads (“iTunes Plus”). They might not work with old and/or off-brand mp3 players. If in doubt, check your device’s manual or search the web.
Apple Lossless (Mac) and FLAC (Windows) are “audiophile” lossless formats which provide CD-quality sound. The tradeoff is that they take up more space on your device than AAC files.