This is the way I would use these (I have added some words to show the context in which the sentences could be used):
1. My favorite animal is dog.x the dog
2. Dog is my favorite animal.x The dog
3. My favorite animal is a dog that I used to have as a child.
4. A dog is my favorite animal to have as a pet.
5. My favortite is the dog. (dog is used as a collective for all dogs)
6. The dog is my favorite animal.
7. My favorite animal is dogs. I like all dogs.
8. Dogs are my favorite animal. (animal (singular) is used as �type of animal�)
9. My favorite animals are dogs. I like all dogs. -- -animals plural - can also be used for My favorite animals are dogs and birds.
10. Those dogs are my favorite animals. Without a defining word before dogs it �s best to use animal (singular), because animal is being used as a collective �a type of animal �
The usual way to talk about your favourite animal is:
My favourite animal is the dog.
