I highly recommend starting with Renoir of the 30s which is one of the strongest decades by a filmmaker in history. Most people will tell you to hit the iconic works - The Grand Illusion and The Rules of the Game - first, but he has other ones that are slightly behind the aforementioned like La Bete Humaine, La Chienne, The Crime of Monsieur Lange, Boudu Saved From Drowning, A Day in the Country, Toni, and La Marseillaise which are all Renoir near-masterpieces...which would be most filmmakers' masterworks.