Troell is good, but my vote for best living "contemporary" director would go to either Emir Kusturica or Julio Medem.  Von Trier shows potential, but his adherence to Dogme95's use of handhelds can make his films very difficult to watch on a theater screen.  Although one can always watch his films on home video, it relegates the role of foreign films to home viewing and takes away from the film going experience.

Six months ago, the answer to this question would have easily been Robert Bresson.