More than one
We often think of dogs as pack animals due to their wolf ancestry, and cats as solitary animals. In either case, when adopting pets, two cats or two dogs are more likely better off than one. In part it is shared species communication, grooming, and other physical interactions, but is also due to the likelihood that they would otherwise spend hours alone each day. Unexpended energy may be spent on destructive activities. This is Uschi and Tanji the day we adopted them, their brother Vladi (above) was born a year later.