Ecu-Extreme close up
You would normally need a specific reason to get this close. It is too close to show general reactions or emotion except in very dramatic scenes.
A two-shot could also involve movement or action. It is a good way to follow the interaction between two people without getting distracted by their surroundings.
This shot is framed from behind a person who is looking at the subject. The person facing the subject should usually occupy about 1/3 of the frame.
This shot helps to establish the position of each person, and get the feel of looking at one person from the other's point of view.
It's common to cut between these shots during a conversation, alternating the view between the different speakers
The mid shot shows some part of the subject in more detail, whilst still showing enough for the audience to feel as if they were looking at the whole subject. In fact, this is an approximation of how you would see a person "in the flesh" if you were having a casual conversation. You wouldn't be paying any attention to their lower body, so that part of the picture is unnecessary.