At the same bitrate, AAC and Opus usually keep speech and music clearer than an older MP3 encoder. MP3 remains the format most players accept without negotiation.
AAC in an M4A or MP4 container is the usual match for Apple and many video tools. Vorbis in Ogg is an open alternative. Opus is strong at low bitrates. The pinned ffmpeg.wasm core may include libopus; the audio converter shows an output only after the encoder list is known where that check runs.
None of these lossy formats should be used as an archival master if you still have the original WAV or FLAC.