Cats. I`ve never had a dog but I used to 'adopt' other peoples' dogs when I was young (usually some farmer's Collie) and we went everywhere together. These days, I couldn`t take a dog for a walk because I couldn`t bring myself to pick up their mess and put it in a plastic bag. That would turn my stomach.
For years I would have said cats but since I have had the pleasure of Willey's presence....most definitely dogs. He has given me such loyalty and love in the last 12 years, I wouldn't swop him for the world.