Why limit yourself to these two breeds? There are many more small dogs. If you get a toy poodle check its temperament they can be prone to nipping. Pugs are prone to breathing problems. I recommend more research on your part.
You can't judge exclusively by breed just how easy a dog is to train to do ANYTHING...There are individuality traits that even dogs have .. just like people...and we all know .. there's nobody stupider than people.