MP3 is widely supported
MP3 files play on most phones, computers, and editing apps. It is a convenient choice when compatibility matters most.
M4A can preserve more detail
M4A is a container often used with AAC audio. At a similar file size it can retain more detail, but a few older devices may need a compatible player.
Choose based on the source
A format cannot restore audio quality that was not present in the source. Keep the original where possible, and only extract audio when you own the recording or have permission to use it.