Neither understands what you see in cats. Dogs do not have problems expressing affection in public. Dogs miss you when you're gone. Dogs feel guilty when they've done something wrong. Dogs admit when they're jealous.
Dogs are very direct about wanting to go out.
You can train a dog. Dogs are easy to buy for. The worst social disease you can get from dogs is fleas. Dogs mean it when they kiss you. A dog's parents will never visit you.