A dog loves you over all else and will never leave your side. A cat is entirely apathetic towards your existence and will rarely bother or comfort you.
Cats, for the love of god, cats.
This new years I had to babysit a golden retriever for a friend, the dog was a saint and was completely well trained, but he was so dependent on me that I had little time to do anything other than loving him. I'm a busy person, I can't afford the time to take care of a dog. Cats don't give a fuck. You can leave your door open and your cat will explore the world, and then return safely because that is where his bed and food are. Dogs are just stupid people with four legs, regardless of love output, whereas cats are independent sociopaths that know when and where to be with you.