I prefer dogs to cats, though I have both.
Having a cat is like living with a roommate, whereas having a dog is similar to having a child. Cats seem to be less expensive to own, also, so that is a consideration for those of us on budgets.
If your life is busy, and you don't have a lot of time at home, it can make more sense to have a cat or two for pets.
Dogs, of course, are pack animals --- they need time with their families, and they need to go outside to potty. If you love dogs, but are away from home hours a day, consider using a pet sitter to give your dog some love, attention, exercise, and a potty break. You'll come home to a much happier family member.