The seventh one is good as well, my list probably goes 5 > 3 > 7 > 4 > 2 > 1 > 6.
If you like the music, make sure to get the compilation soundtrack (Ongakushu), it has one or two long tracks per movie that incorporate bits and pieces from all of the BGM. The first one for the fifth movie is one of my favorites.
The song you linked is part of the "Thanatos" track on that album, which is all BGM from the first movie.