In my opinion dogs are better than cats. I will tell you of why in my opinion dogs are better than cats. I will tell you some disadvantages of having a dog. Also, I will tell you some disadvantages of having a cat.
One advantage of having a dog is that they are smarter than cats. Dogs are smarter because if someone is breaking into your house, a dog will protect you. As of a cat, it would probably just watch the intruder or go back to sleep. There is also more than one reason why dogs are smarter than cat. One of my personal experiences was that my dogs were staying the night at my aunt's house and my aunt accidentally left the garage door open. Somebody got in the garage and stole some things. After that the dogs barked and the person left.
One more advantage of having a dog is that they are more playful than cats are. You can teach your dog to fetch and play with you. If you throw a ball to a cat it would probably watch you go fetch it. If you have kids, than dogs will play with them. There is a wivestale that a cat would suck the air out of a baby's lungs. Personally, I do not believe it.
If you have a dog, it could exercise with you. From a personal experience, I have seen people (mostly men) running with their dogs. If you run with your dog, you will push yourself because a dog will constantly want to run faster and faster until it runs out of energy. Most people that run with their dog could put them in a dog sports event. It would benefit both of you.