The one upstairs is nicer, quiter, a bit tastier but much much more expensive. Les Chefs De France downstairs is nice also, its really your choice. They are both great restaurants. Maybe use the reviews section of this website.
There are 2 sit-down restaurants in France. Chef de France and the Bistro de Paris. Both are excellent!
Chef de France is open for lunch and dinner. You feel like you are sitting in a Cafe in France. Ask for a window table -- and people watch. Chef de France is a bit less expensive than the Bistro.
The Bistro de Paris is on the second Story of the French Pavillion. It is more formal -- but formal attire is not required. It's currently now only open for dinner. It's very elegant. Some say they have requested a table by the window to view Illuminations. We have always dined prior to the start of Illuminations.
Both had excellent food, service and atmosphere. Here is a link to the menu of both.
PS. Keep in mind there is a wonderful French bakery (counter-service) and the shops sell samples of wine.