The preferred preservation formats for high quality audio are wav (uncompressed) or flac (compressed but without loss in quality).
For everyday use and lower (compressed) file size, aac is considered better quality than mp3, which is widely used for streaming and mobile devices.
To hear what audio data gets eliminated by mp3 compression, check out Ghost in the MP3.
The Preserve This Podcast team presents illustrated guidance on organizing, backing up, and creating metadata for your podcast files (and audio content in general), with links to interactive exercises.
Preservation container formats for digital video (which also contains audio files) include avi and mov (Quicktime).
For lower file sizes, mp4 is a popular and widely supported container format for the H.264 video compression codec and aac audio codec.