The OGG format is an open and free standard with no patent and license restrictions. Nowadays, there is no clear standard for this format. Also you should understand that OGG is just a container for video and sound, and may contain streams encoded by different audio and video codecs.
AC3 or Dolby AC-3 is a data format file where six audio channels are compressed by the AC3 codec, also known as Audio Codec 3. The AC3 format is used for the following audio formats - DVD, Blu-ray, cinemas and game consoles. To play the full surround sound of the AC3 file signal, you need a device that supports Dolby Digital technology.