Auto-area AF does not allow the user to specify the subject but the camera decides what is the subject and focuses on it. Furthermore it frequently switches to a different subject when there are multiple potential subjects (e.g., people) in the frame. 3D tracking uses the user's input to identify the main subject and sticks to it as the subject moves in the frame. Auto area AF is continuously evaluating what is the most likely subject and often cycles through the options that the camera has identified. I believe it uses the RGB matrix as does the 3D tracking, and both are capable of prioritising faces as well, if the user sets this option. Group area AF also seems to use the RGB matrix (as it is only available on cameras with high resolution RGB matrix sensor) but the choice is restricted in area to the group. It can use face priority in AF-S mode. For me the dynamic area AF is problematic and for now I have restricted the selection to single point AF, Group Area AF, 3D tracking and Auto Area AF as dynamic is so eager to focus on background features if the point slips even slightly or the subject is too small.