The Idiots is certainly an acquired taste - it represents Von Trier trying to make a film to a strict coda, which he named the '
Dogme 95 Manifesto' and is definitely much more of an experimental work than most of his other films.
Antichrist is another that tends to split audiences, although I do really like it. I'd highly recommend Von Trier's 'E' (or 'Europe') Trilogy; The Element of Crime, Epidemic, and Europa; all of which are excellent and a little less divisive and controversial than either The Idiots or Antichrist. Add to those Breaking the Waves, A Dancer in the Dark, and one of my personal favourites, Melancholia and you have a impressive sample of films from one of the best directors still working today, in my opinion.
However, despite his impressive feature-film resume I still rate Von Trier's TV series 'Riget' (The Kingdom) as his best work to date.