Serris, when you said LBT9 I got my numbers mixed up and thought you meant The Great Longneck Migration, and at that point I totally agreed with you.
Then Malte pointed out your mistake, and now I have to abstain, since I haven't seen that movie yet. The Youtube version of Noone Has To Be Alone is pretty good.
I can't say I've ever heard any voice actors whose singing I considered "Bad." Some songs I didn't like, but it wasn't because of the singing, it was just the topic or the execution of the song (Like "The Mad Song" or every song from LBT13).
My favorite part of any song is in "Bad Luck" (LBT7) when Cera sings "When a Sharptooth finds you All alone" and audibly quavers the 'all.' I can't imagine how the voice actress was able to imply shock like that.