What you look for in a breeder is sadly, in this breed, going to depend on what your aims and goals are.
In this breed, there is a pretty big division between the working and the show lines, which I do regret.
My priorities are a healthy, stable animal with a proper working temperament and good drive, and lastly perfect structure. I am of course concerned about structure, but I am not looking for a show dog - my main venues are performance ones, so I want someone who is also similarly interested in those things.
My previous dobes have all been rescues, but when I opted to get a pup from a breeder I knew I wanted someone who was concerned about health, knowledgeable about the breed, who personally worked their dogs and could tell me about their temperaments and drives, who was concerned about structure and how that interplayed with working abilities - I wanted it all. I think I got it, or as close as I could at this time. Berlins a nice looking bitch - she'll never finish in the AKC, and she has her faults - but she's not ugly, and she's very pleasing to look at. I got someone who above all is a good friend, but knows the history of the european lines they are breeding, knows about training, still shows their dogs in the AKC breed ring (the same dogs that train in bite sport), and is a huge advocate of health and education. and as a bonus, close by enough for me to strike up a lifelong friendship - i really lucked out. They are very active in our local clubs (both DPCA and UDC), constantly looking at ways to do education (this year our dobe club has had alternative medicine talks, we're hosting a health clinic, we were the first chapter club in the dobe breed to host a working sport trial for the AKC, we pair up with our sister UDC club, we host a huge independent specialty that includes obedience and rally - and they are a huge part of that).
above all, i love the dog i got from her - she's a hoot to live with, and she's really a great working dog - which is my priority.
freestack at 7 months (maybe 8?) last year.