I prefer dogs, and if I have a chance to raise one of them I'll choose a dog. But I also like cats. They are difficult to be familiar with, but when you become familiar with them once, cats are really affectionate!
Maybe it is out of point of this discussion, but if I have more choice, I prefer parrots because I keep a parrot in my home. She makes so many troubles with her beak, but I forget everything about her mischieves when she follows me looking at me with her head tilting.