Optimus Prime:
Remains calm, even if he did find an animal to be cute or adorable. Remember, Prime keeps his emotions in check. He prefers not to treat animals as animals, but as living beings. Because that's what they are.
Bumblebee:
Bee is fascinated, to say the least. He's always thought that the only creatures on Earth were humans. He also likes the fact that animals cannot talk as humans do, he believes the eyes of an animal have the power to speak a great language. Very much like himself.
Ratchet:
He sees it as another bag of flesh he must avoid stepping on, which is a bit more difficult since they are smaller. But sometimes, you need to look at life from a different perspective. He gradually warms up to having an animal around, they're much more obedient than Y/N and Miko, anyway.
Smokescreen:
Loves it. Sure, he isn't as ecstatic about Earth as any other Cybertronian, but he appreciates the small, beautiful things our planet has to offer. He believes everyone has more to learn about animals, than animals have to learn about everyone else. Also, he likes the super fast one with the cool spotted fur "finish".
Megatron:
Respects them more than humans. He's taken a liking to fierce animals that stand their ground, and others that defend their territory. He thinks it is just like man's vanity and impertinence to call an animal dumb because it is dumb to his dull perceptions.
Soundwave:
Soundwave has a familiarity with creatures such as these, as he has Laserbeak. Some also remind him of previous deployers like Ravage, Frenzy, and Rumble. He appreciates some extra company, but he chooses not to get too attached. Loyalty first, after all.
Knockout:
Tolerates them, depending on which species. Knockout can either be okay with having an animal around, or not accept it one little bit. His favorite are the Felis Catus, as he admires their proud, yet slightly weird way of cleaning themselves.
(Bonus picture, hopefully it's there now)
Told you he loves it.