I find this to be a difficult choice. I consider all the 1959-67 films to be parts of a whole, so to speak. The best place for anyone to start is with A BOUT SOUFFLE. The posts to this list seem to be subjective so I will be personal and plug DUEX OU TROIS CHOSES [TWO OR THREE THINGS I KNOW ABOUT HER] as the one Godard film that encompasses all his thoughts and theories. The film still embraces the remnants of a narrative structure, it utilises Godard's favourite metaphor: prostitution and it points the way to socio-political-philosophical theorising . Above all of this, the film still remains a film about film. Actors act and discuss the reality of life and films. This film itself is seen as a product of this same reality. Easily found on video: get it!