AAC or Advanced Audio Coding is an audio file format with losses. It was designed in 1997. as an MP3 successor with improved encoding quality. Its main advantage and difference from MP3 is a great efficiency of encoding at both constant and variable bitrates.
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.