I think adding face portraits (only the face, big and clear on the left side of the box) is easy enough to apply so I go for them. But then, you can add the option for the players to turn on and off a full body portrait (if you ever add clothing mechanic to the game this allows the players to take full advantage of the a full body portrait too).
And as for what version of the full body I like... I think a slighty different version 4 is the best. Make the character bigger and keep the chatbox that size, I don't know if it would be too much of a hassle, but add the character in a way they cover juuuust a bit of the side of chatbox, in my opinion it makes the dialogues more pleasing to look at, plus it makes the character seem more alive as it is interacting with the chatbox.
