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.