That is a hard choice... I love the original Joker minifigure from 2006 as it is so nostalgic to me. On the other hand I also like the Joker design from 2012 up and I defenitely love the LBM interpratation of the character.
I don't really like the face of the dark knight version though.. it is just weird (imo).
In the end I think I have to go with the classic one (2006) but the LBM version is on a very very close second place.