What guard dog is best for a single, first-time owner in an apartment?

Great question! This is a bit of a tough question in that a number of breeds of dogs who are good guard dogs are also difficult. For example, a German Shepherd. Good guard dogs, but require a lot of training and are not for a first time dog owner. If you don't know how to handle them, they can be aggressive to humans and small animals. They are also high energy dogs. Personally, I would recommend a Golden Retriever. They are absolutely lovely dogs, extremely loyal, very easy to train, excellent with humans and small animals, and if need be, could defend the owner. I had a Golden for 12 years, and she was honestly the best dog I have ever owned. So sweet and caring, but I knew that if I was ever in trouble, she would defend me. Goldens are a large breed dog, and large breed dogs can be intimidating to strangers. My Minnie would bark if someone came to the door and knocked, but otherwise didn't bark much. Sometimes a bark is enough to scare someone off. I would look into getting a Golden Retriever for the reasons I listed above. I hope this helps!