The Lab was the hardest to train. The Ridgeback was notably easier. The easiest of all was a GSD mix rescue. It's almost like he came pre-programmed.
My son had a Cavapoo (actually a Cava-cava-poopoo). Small, yappy, and not very obedient, but that is prob more a reflection of her lack of training.
Another son had a pitbull/husky rescue that was a free spirit! Very difficult to train.