To answer the original question "How do you judge a good bird dog?" I will try my best to answer that question. I judge them based on a few critical components that are necessary for a bird dog.
1. Drive. If they do not run and hunt for scent you are limiting your ability to find birds. The more drive they have, the more birds they will find. You cannot train drive into a dog it must be bred into them. You can control it but you cannot manufacture it in a dog that doesn't have drive. Want a good bird dog, find one from parents with drive!
2. Trainability. All dogs can be trained but talk to anybody who trains dogs regularly and they will tell you some dogs are more bidable than others. Want a good bird dog, find one that takes well to training.
3. Retrieve. Because I hunt with retrievers I need my dog to retrieve. Retrieving is part drive, part breeding, and part obedience! Yes delivery to hand is about obediance. Many guys will say they are very obedient and hunt close but won't retrieve to hand. Treat it like obedience and see how much better your dog becomes.
4. Birds. Many days I shoot my limit when others do not, why? Good bird dogs. At the end of a hunt I can usually say I shot more birds than anyone else in the group. Not because I am a great shot, but because I have dogs with drive, trainability, and retrieving obedience.
Tha's my .02 on the judgement of a good bird dog. Field trials and hunt test put a standard on the table that you can measure a dog against. Typically the guy who brags about his dog before the hunt usually has a mediocre hunting dog. The one who lets the dog shine in the field and waits for the group to respond to his dogs ability usually has the better bird dog.