I have two favorite episodes.
My first one is from season one (dont know the name). It's the one where Will and Carlton get arrested for driving someone's car to their mansion cause they took a helicopter. I love how the other person in jail with them sings Let My People Go
My other favorite episode is from season four. It's the one where Will's father came back. The ending of the episode was very dramatic. It showed how good of an actor Will Smith is. He's great in comedy as well as drama. I think he really showed true emotion in this episode.