After 2000? They've done Hail Caesar, No Country for Old Men, A Serious Man, Inside Llewyn Davis, True Grit, The Ballad of Buster Scruggs, Burn After Reading... all of which are wonderful, to one degree or another.
A Serious Man and Hail Caesar would be my picks for the best of those.
The Ladykillers and Intolerable Cruelty I only watched once each on release and haven't revisited. I consider them the only true duds of their careers. They're not terrible, but they feel like someone else trying to make a "wacky" Coens film.