i have a feeling most of the votes are going to go for dogs with people on this board. but my vote went for a dog too. the loyalty, intelligence, playfulness. you can't find that in a cat. well maybe some of that, but it's not the same.
.Cat, fun to intimidate. Also if they catch there own food leaving it outside, leave bodily waste outside, sleep inside, and dont need for me to take care of them then I love them. If your thinking that cannot happen with a cat, well you're wrong. We got at least one cat who is like that.
I bought an algae eater (catfish) to clean my fishtank a few years back. He was only a couple of inches long. He grew to be about 3/4 of a foot, and the most disgusting thing to look at. My dad took him out and flushed him down the toilet (it almost flooded the toilet!)
I hope my dog doesn't see this but I voted for the fish too. You don't need to take them for a walk, they don't make noise and annoy the neighbors, and you can keep a whole bunch of different kinds in a small space.