It depends on whether you are looking for the best selling, the most highly regarded or the most expensive chocolatier.
It was always thought that the best chocolate came from Belgium, and many of the world's most loved chocolates are still made there. However, according to at least one list the best chocolatier in the world is from Switzerland. This is the Zurich company Teuscher, best known for its champagne truffle and exported all over the world. You can see the rest of the top 10 here.
If you go by price, there is actually a box of chocolates - called simply Le Chocolate Box - which costs $1.5! However, it does contain a lot of actual jewels as well as sweets. THe next most expensive is a mere $10,000.