Draggon was an American Bull Dog. He was easily the most obedient dog I have ever known. Also the most loyal and the most protective. Especially when there were children around.
Several other larger breeds have been known to be very protective of children, like Pits and Shepherds, but both are known to have a temper and a short fuse. And honestly I just wouldn't trust them around my kids.
A Bull Dogs most dominant trait is loyalty.
Some breeds are labeled as being very smart and trainable, like the Poodle. And some are known to be hard to train or stubborn, like the Chow Chow or Husky. But, I believe that the success in training of a dog lies within the owner/trainer. If you put time and effort into training a dog in a loving way, you'll reap the rewards. Some smaller breed dogs are disobedient in my opinion, because they are spoiled by their owner, and never properly trained to have good manners.
I have to say German Shepherds are very obedient, if you raise them from a puppy they are extremely loyal and obedient. They do sometimes look tough and their bark is kinda scary but mine is the biggest sucky baby i've ever seen-she will however protect me if i need it. I would think the most disobedient dogs are the smaller dogs. I also had a poodle and a bison and they were always kind of lost in space. Cute though.
My first dog was an Australian Cattle Hound and German Sheppard mix, and was one of the most obedient dogs I have ever seen. My parents taught her a lot of stuff, and she followed their instructions like a soldier taking orders on a battlefield. My personal dog, now that I'm an adult, is one of the most disobedient dogs I've ever seen. She is a Dauchsund/Chihuahua mix, and has a mind of her own. She only responds to one command and that is "STOP!", and she'll stop doing whatever it is that she is doing (like tearing the spines off all the books on the bottom shelf of my bookcase) and run away.
Dauchsunds are hard-headed dogs, not recommended for a highly-trained pet.
Golden Retrievers, Labradors, and German Shepherds are most likely to be chosen by guide dog facilities, although other breeds, such as Poodles, Collies, Vizslas, Dobermans, Rottweilers, Boxers, Border Collies, and Airdale Terriers may also be selected. This means that these are probably the most likely breeds to start with if you are looking for an intelligent and trainable dog.