The question might require a bit more detail. If we are examining the basic concept of who embodied obedience, there can be many candidates for this. In my mind, I am not sure that there is anyone who represents obedience and loyalty such as Hanuman, who is willing to do anything for his master, Lord Ram. There is little else that can compare with the level of devotion Hanuman shows Ram. Whenever Lord Ram is in need, Hanuman is there to help. He worships his Lord and is willing to assist him and Mother Sita at any and every time. A great example of this would be when Lord Ram needs to find Sita. Hanuman does not hesitate to fly to Lanka, and find Sita, telling her that her husband looks for her. There are other instances where his obedience and loyalty are on display for all to see. Certainly, disobedience would be predominantly seen in Ravana, who represents a lack of obedience when he abducts Sita and wages all out war against Lord Rama.
Ramayana is a book having scores of characters and most of these characters display high degree of obedience. This Applies also to the demons. For example, Kumbhakarna, younger brother of Ravana, believes that it was unwise for Ravana to act against Rama, yet obeying the orders of Ravana, he joins him in his war against Rama.
I can think of one significant incident of disobeying described in Ramayana. But this is just an exceptional behaviour of the character, rather than regular disobedient nature. In this incident, Lakshmana instructs Seeta to not to cross a line drawn by him, when he has to leave her alone in their hut in the forest, to rush in aid of Rama. However Seeta is persuaded by Ravana, disguised as a ascetic, to cross the line. This makes it possible fro Ravana to abduct Seeta.
If it is a matter of deciding who among all the character was most obedient, I would choose Rama. He has displayed obedience to his father, his mother and step mothers, and his teachers.
Hanuman, definitely represents the finest example of devotion to the all mighty Lord. However, devotion, loyalty and obedience are not synonyms. While I cannot think of Hanuman ever being disobedient to Rama. However, I do not think Ramayana present any incident which emphasizes his obedience in circumstances where it was difficult to decide the right course of action..
Wouldn't you all agree, Lakshmana was obedient to his father Rama and his mother Sita throughout the book?