MOV is Apple's homebody: gorgeous on a Mac, awkward everywhere else. It was born in 1991, Apple's QuickTime team, and its real weak spot is traveling: Windows, Android and the web would all rather meet an MP4.
MP3 is the format that taught music to travel: small, scrappy, and welcome absolutely everywhere. MPEG-1 Audio Layer III. Perceptual coding: it throws away the parts of the signal your ear is least likely to miss. That makes it the right destination when what you need is playing on anything with a speaker, from new phones to twenty-year-old car stereos.