Neither understands what you see in cats. Dogs miss you when you're gone. Dogs feel guilt when they've done something wrong. Dogs don't criticize your friends. Dogs admit when they're jealous.
Dogs are very direct about wanting to go out.
Dogs don't feel threatened by your intelligence. You can train a dog. Dogs are easy to buy for. You are never suspicious of your dog's dreams. The worst social disease you can get from a dog is fleas.