What is AIFF?
AIFF is Apple's uncompressed audio format - WAV's counterpart from the Mac side of the world, and still what Logic and older Pro Tools sessions use. It stores its sample rate as an 80-bit extended float, a piece of 1980s exotica most converters get wrong.
What is OPUS?
Opus is the best-sounding lossy codec at low bitrates by a comfortable margin, which is why it carries the audio in nearly every voice and video call you make. It is royalty-free, it handles speech and music equally well, and it is usually wrapped in an Ogg container.