Sure, the Doctor can have all the knowledge in the universe, but he can still learn from other less evolved species, and he did from many of his companions. And he did from companions like Rose and Donna. Stuff like courage, compassion and to live in the moment. They made him laugh a lot. They were able to move the Doctor deeply and be less rigid with his time laws, and they also surprised him when they risked everything to save him. Pets can't carry a conversation with you like humans. And I think dogs and many animals are very smart. maybe the Doctor likes us because we are more simple.
Agreed.