eh opposite opinions there. I love MCR but Cancer is easily my least favorite song by them. I still sorta like it and don't skip it. I don't hate cancer though. The thing I like about Sing though is that it shows Gerard's vocal strength as he rise's in octaves. I don't think sing is the best song they have ever wrote but I think sing gets way too much hate because it was used on glee and american idol. I really doubt those songs were written with that purpose in mind.
Both those songs are on the bottom end of the MCR songs I listen to though.