I would suggest finding both GSD and Doberman rescues in your area if you are serious about doing this the right way. Contact both rescues, go meet the dogs, and see which "clicks" with you. Nobody here can tell you which breed will suit you better, you have to make that call.
If you find a good rescue, they will often also be able to point you in the direction of a good trainer in the area. In the meantime, if you're interested in learning more about training check out:
http://www.leerburg.com for some ideas. Maybe get some of their DVDs to watch and learn from.
I would strongly suggest you go for a rescue dog. Both Dobermans and GSDs change a lot between the time they are small puppies and adults. Even to very experienced people in the breed it is often hard to tell what "personality" the dog will mature into. Since you're looking for very specific qualities in a dog, a rescue will likely be able to match you with an adult that has those qualities. They are experienced in the breed and know the dogs they have available and will be able to match you with one who will suit you. If you buy a puppy, even with a good breeder, you are taking the risk that the dog you buy will grow up to lack the qualities you are looking for.