What is your favorite Rin and Len song and why?

My favorite song they sing together is Migikata No Chou, also known as Butterfly On Your Right Shoulder. I love the concert version because Len can remix his voice XD. I also love the songs Servant of Evil and Daughter of Evil, which go together and tell a nice story. As well as Prisoner and Paper Planes, Paper Planes is the answer song to Prisoner. It actually made me cry but I still loved it. Plus, I just Love Rn and Len, especially Len!!!