It really depends on you and your life style. Cats are more independent and can go for long periods without much attention. You can leave for 12 hours and not worry about coming home to a mess. A dog on the other hand will need to have gone out in that amount of time. And even with dogs you need to be aware of the energy level associated with the breed. I have boxers and I think they are the best dogs, however they are not for everyone. They are high energy and need at least an hour of exercise a day. Greyhounds only need about a 20 minute run and are good.