i voted for vain it's my favorite moi dix mois song EVER, its perfrectly heavy and elegant. the drums are wonderful and the guitar isn't just 2-3 chords. xD
...To be honest, Vain would be the best PV, because it's like.. the average song of the album. There's both elegance and heaviness on the song, which would be a nice balance, instead of only shining light on one facet of the band.