To add to the list of very smart dogs...
Belgian Malinois (much smarter than GSDs, and faster too)
The Havanese - a small dog almost done in by Cuba’s Castro regime, often used in circus acts.
After years of large dogs, my friend bought 2 "Havamalts" -- a cross of Havanese/Maltese. She's having so much fun with those little guys, and she is training them just like she did her big dogs. They are taking very well to it.