What is the smartest dog?

Intelligence varies among individual dogs.  However, some breeds do tend to be 
smarter than others, especially in terms of how easy they are to train and how 
well they obey commands.  Here's a page which mentions three different aspects 
of dog intelligence and ranks breeds of dogs by intelligence, based on a survey 
of dog trainers.  These rankings are taken from a book called "The Intelligence 
of Dogs" by Stanley Coren.  The same list appears on a number of different web 
sites.  It lists Border Collies as the most intelligent breed of dog.
 
http://www.petrix.com/dogint/intelligence.html

The top ten smartest breeds of dogs according to this survey:

1 Border Collie 
2 Poodle 
3 German Shepherd 
4 Golden Retriever 
5 Doberman Pinscher 
6 Shetland Sheepdog 
7 Labrador Retriever 
8 Papillon 
9 Rottweiler 
10 Australian Cattle Dog

My impression is that you were asking about breeds, not individual dogs.  If 
you wanted to know who the smartest individual dog in the world is, I don't 
think there's an answer.  Unfortunately, I don't think there is a Dog 
Intelligence World Championship yet.

Thanks!