I like the 2 pet lists although, of course, my list is different. Then again will so many pets to chose from it is not surprising. My list:
Mr Pericval a pelican from Storm Boy (1976), this choice is very much based on my childhood memories as is my next choice
Mij an otter from Ring of Bright Water (1969), many many tears fell over this one
'Beachball' the alien from Dark Star (1974), it is probably sentient, but it is kept like a pet, so it makes this list
Lassie a dog, like you did not know
Grommit a dog from the Walace and Grommit films