Every audio format is a trade-off between size, quality, and where it plays. Here's the practical map — which one for which job, no allegiances.
The formats in one breath each
MP3 — the universal donor. Not the most efficient anymore, but plays on everything manufactured since the late 90s. When in doubt, MP3.
AAC/M4A — MP3's successor. A bit better at the same bitrate, native to Apple everything, standard in video. Raw .aac trips some players; .m4a rarely does.
Opus — the technical champion. Best quality per kilobit by a distance, powers WhatsApp and Discord; hardware support still lags, so convert to MP3 for the car.
OGG Vorbis — the open veteran. Patent-free, loops cleanly, beloved by game engines; consumer devices mostly shrug.
FLAC — lossless, ~40% smaller than WAV, tags and art support. The archival format for music collections.
WAV — raw PCM, no compression, no real tagging. The interchange format of studios and samplers; wasteful for listening.
Quick chooser
Sharing with unknown devices → MP3 192 kbps. Archiving CDs or masters → FLAC. Editing or sampling → WAV. Voice notes and podcasts → Opus or mono MP3 64 kbps. Game audio → OGG. Apple-ecosystem library → M4A. iPhone ringtone → M4R (a renamed AAC with rules — our ringtone maker handles them).