for security purposes which dog is the best?

I would have to say a Rottweiler...they are great dogs and fierce too

I think German shepherd is a good choice. They are loyal and can be trained easily. They are mostly used as police dogs.

I have a doberman. Either one isn't mean and very friendly but someone that doesn't know them step back when they bark. My female is extremely friendly but when I am home alone with my granddaughter she is between the door and us. Someone tried to come in the back door one night when we were home alone and whoever it was left quickly but her hair was standing up. I would never have thought she would be protective because she is shy and scared of most things. She loves people though. My male is very friendly. He was gave to me recently and will stand on his back legs to look people in the eye. Something I am working on to break. He greets everyone with this behavior and it unnerves people. If I wanted a gaurd dog I would put my money on my 6 lb poodle. He is very friendly but don't raise your voice or hand to me or my granddaughter. He also moves like lightening and is in and out between feet. You have to watch yourself to keep from falling. Biting isn't something he does to be mean. He will grab your pant leg or shirt sleeve if you haven't been paying attention to pull on it to tell you to pay attention. Big dogs scare people because they can do major damage with one bite. Little dogs usually bite quicker but do less damage and people are not as scared of them. Though I have seen where some little dogs have done some major damage to people.

I'd say big dogs like rotweillers, dobermans, and german shepards.

There are so many factors in deciding on what dog is best. Dogs are what you teach them. Of course the bigger dogs usually are better for warding off people, but you also have to have the room for them either in your house or outside. I have a black lab and a bull mastif. My black lab is smaller than the mastiff and barks at everything that comes near the house. The mastiff is intimidating looking because of his size, but doesn't bark unless something is absolutely not right. It all depends on the dog's personality and how you raise it.

Any dog can be trained to attack. There is no "guard dog" that is guaranteed to attack or defend your house. I got my best defense out of my dauschund. My 10 lb dauschund. My lab is scary looking, but is scared of a lot. My spaniel mix dog hates the garbage men, the meter readers and the postal woman. Your best bet is to adopt a dog from a shelter and just send it to training schoool. A lot of thieves and crooks have been interviewed on TV and they have said if they hear any dog barking, whether it's a golden retriever or a chihuahua (the Taco Bell dog), they'll pass that house up and move on. Good thing. I've got 7 dogs.