I would think anything other than the conventional dog, cat, or bird wouldn’t make the list of best pets. A horse is a beautiful animal, but it’s difficult for me to consider a horse a pet. It’s more like a companion, or 4-legged colleague.
I’ve seen the YouTube clips of “pet” mountain lions and wolves and deer, etc. But in general, worst pets would probably be a ferret, snake, most any wild animal– any big cat, bear, wolf, chimpanzee, alligator, wolverine, shark, jellyfish, or a tick.
And I’m sure there’s disagreement on most of this. Except maybe the tick.
3 Cents' 