What is MP3?
The format that made digital music portable, and thirty years on it's still the safest bet that a file will simply play - any device, any car, any decade-old bit of hardware. It's lossy, its patents expired in 2017, and no browser has ever been able to write one, which is why encoding it here needs LAME.
What is AIFF?
Apple's uncompressed format, the Mac counterpart to WAV, and still what Logic and older Pro Tools sessions expect. Its one genuine oddity is storing the sample rate as an 80-bit extended float, a data type almost nothing else in computing still uses.