If I HAD to pick one I would say France. It's just a personal fav speaking French, smelling the yummy pastries, the huge movie they play, the wine, the perfume and the beautiful landscaping.
Every country is unique and has plenty to offer. I was on my 4th trip last year and finally made it "in" some of the countries to do things like ride Rio de Tiempo, explore the shops and take time to watch the various performers. Some of the stuff I didn't even know exisisted!