What is OGG?
Ogg Vorbis is the patent-free lossy format that came out of the free software world. It compresses well and it has always been unencumbered, which is why games, Wikipedia and open-source projects reach for it while consumer hardware mostly ignores it.
What is AAC?
AAC is MP3's designated successor and the audio in most video: YouTube, streaming services, broadcast and virtually every MP4. At a given bitrate it beats MP3 audibly, particularly below 128 kbps, and every phone and browser decodes it.