For me, France, hands down. France has a superb network of minor secondary roads with minimal traffic. Also quite a few canal trails. There are extremely varied landscapes and a greater choice of topographies than you'll find in Spain or Italy. It's easier to find campgrounds, little hotels, & restaurants in remote areas of France than in remote areas of the other 2 countries. Petty crime is a bigger problem in Spain than in Italy or France, though it exists in all 3 countries. Restaurant hours in Spain and shop opening hours in Spain can be problems. France has more areas (in the north, esp.) likely to be too wet, whereas Spain has more areas likely to be too hot. Topography overall is most difficult for cyclists in Italy. Another aspect to consider: Do you speak any French, Spanish, or Italian? If you speak one of them, it will add to your enjoyment in the respective country.