They are useless. It's just there because people really want HUGE AMOUNT OF STUFF. Why do you think the completion percentage is 1000%? So people can go WOW THAT IS A HUGE AMOUNT OF MAP TO COVER!!!111111
Portrait of Ruin has so much lost potential.
Billie Jean is great too. After my two aforementioned favourites, I like Bad, Beat It, Billie Jean (they all start with Bs), Another Part of Me, The Way You Make me Feel, Dirty Diana, etc. almost equally.
I suddenly like you a lot more.
No, Thriller is amazing. Don't even compare it to Marth.
But really, most all of the songs off Bad and Thriller are great and it's no surprise if any one of them is someone's favourite. My personal favourites are Smooth Criminal and Thriller, but I love a lot of others too.