Cat. I have five. No need to go for a walk, won't disturb you, will use the litter box on their own (you don't have to teach them to do that)... Just adopt an adult cat. Two of my cats were adopted already grown and they're just as affectionate as the others (which is greatly affectionate, btw). It really comes from their personalities plus your input. Don't forget to neuter/spay the cat.