For whatever reason, a lot of the episodes I enjoy re-watching are in season two. Most of these episodes revolve around Juubei and Kazuki, my two favorite characters in the series. The main reason I enjoy watching these episodes is because they make me feel good and bring back fond memories of watching this in middle school.
I think there are a number of reasons why people like to re-watch anime series. Some people watch an anime over again for nostalgia, others because they need their memory refreshed. I tend to lean towards re-watching shows like Saiyuki, Sailor Moon, and Getbackers that bring me nostalgia and make me smile.