I think JD is INFJ, and I will tell you why I think so. When people use their introverted intuition, it can often a self-narration like what JD does in every episode. Introverted Intuition also makes people have visual imagery, much like JD's daydreams. Extraverted Feeling is very JD. He is very emotionally open, which is true about many INFJ's. For example, he yearns so much for that hug from Dr. Cox, and he isn't ashamed to hide his feelings from Turk.
INFP's, INTP's, ENTP's, ENFP's Have Extraverted Intuition, which is not usually in the form of daydreams.