Nice Kenny: This is Kenny in the beginning. He cares about the rest of the people and is a smart, capable leader. He focuses on the well-being of the group.
Asshole Kenny: After the meat locker, he begins to hate people and focus only on survival. He steals the food from a car of starving people. If you didn't help him kill Larry, he abandons you to die in the drugstore. He chooses to let a girl die in the street, leave Lilly behind and he's mean to Clementine.
Grieving Kenny: After Duck and Katjaa died, Kenny became a one-track man. He is either grieving for his family or focusing all his attention on one thing (the boat).
Repentant Kenny: Kenny gets like this for only a few moments. He's either like this when Ben explodes at him, or when he sees the dead couple. He is focused on getting clementine and improving himself, and really ends on a high note.