My daughter flew Air France to Dubai via Paris, and back to Manchester direct with Emirates both in Y class. The aircraft from Paris to Dubai was a B777 as was the Emirates flight back to Manchester. In her opinion the Air France flight was far more comfortable and the food and service much better than Emirates.
However, the Air France B777 she travelled on was the version with 3-3-3 seating configuration and 18" seat width. Other Air France 777's have 3-4-3 configuration in Y class with only 17" seat width.
The Air France A340-300 fleet have 18" seat width in Y class in a 2-4-2 configuration.