As far as sex preference, it really depends on many factors as to what will work best in your situation. If you have young children or are inexperienced with dogs in general, I would recommend that you start with a bitch. They are a little smaller and often settle down a little sooner (this is just in general.......every dog is different). The individual personality of the dog has a lot to do with it also.
Your best bet is to analyze your own personal situation, find a good reputable breeder and let them pick the dog that will be best for you. I don't know where you are located, but to find a good breeder the best place to start is the DPCA (Doberman Pincher Club of America) website. Many good breeders do not have a website and you won't find them on the internet. You will find a lot of slick commercial greeders and back yard breeders on the internet..... that might answer your question about the breeder you mentioned 
You might also want to look into Doberman rescue if the idea of skipping the puppy stage is appealing to you.
Keep in mind that this breed needs a lot of attention, tons of training and exercise. A fenced yard is pretty much a must have. They are smart and will take over your house if you let them. Before you buy, you might want to read a good book on the breed. I recommend " The Doberman Pinscher: Brains and Beauty" by Rod Humphries and Joanna Walker. It is a really good introductory book to the breed.