They are all different.
Why is temperament testing so important? Many people or breeders don't think that it is; they allow their new puppy buyers to pick, first come first choose. But most people have no idea what they are looking for. Sure, they have an idea of the perfect Lassie soon to be in their life; but sadly that doesn't often end up as planned. What they want and how to choose it comes from experience and new puppy buyers don't tend to have that. Choosing the wrong breed and/or the wrong dog within a litter happens a lot.
Within a litter of puppies there are many different temperaments; there in-lies the problem. Which puppy would best suit your family and lifestyle? If you have one or more dogs already; then choosing a good match is more difficult. You have personalities to match up. That said you are the leader, the boss of the pack and you have to live with each one. So choose wisely and if you can, go with a breeder who does temperament testing and knows their litter extensively. Each puppy is very different from the other. Even in a very "even" litter there are differences.
I was looking at Elsa yesterday as she stood watching out the living room window. She was watching for lizards; which has paid off for her several times this summer. Luke use to do the same, as did Tilley but they were all very different. Tilley was very high drive; crazy style, high drive. This high drive created an issue with shadow chasing. Once I realized this OCD issue I very quickly moved it to an outlet that I could control; and Tilley became an amazing Frisbee dog. Tilley was a high energy dog that was very happy to lay on the couch as well. A nice combination. She had a very accessible "off" switch. But even with her high energy and high drive she was not highly interested in playing. She played a bit but she was much more interested in her chase activities. If she was involved in a chase she would completely ignore anything around her.
Comparing Elsa's drive to Tilley's, they are very different. Elsa has extremely high drive but is much more controllable. She has a high drive to chase but does not zone out. Her energy level is probably higher than Tilley's was. She can go all day without batting an eyelash; and if there is anything going on as far as action, she's in the mix. She loves to play more than any dog that I have known and adores her friends. So you see, even though Tilley and Elsa may have scored very similar in the drive section of a temperament test, they were and are very different.
Luke had drive but not crazy drive. He was an amazing retriever but did not want to participate in the activity all day long like the girls did and do. He was reactive, meaning that every emotion he had was bigger than most in outward behavior. Whatever Luke was feeling, you knew it. Not much got past him; but nothing gets past Elsa. She is hyper sensitive to anything and everything going on around her. She is a need to know type of gal; much like I am. :)
When I temperament test, I read between the lines as well as the score the actual tests. This of course is where breeder knowledge of a litter comes in as well. I often chat about my "between the lines" thoughts with the breeder and we discuss each puppy as an individual. A puppy may be the most active in a litter; which to the average puppy buyer looks like fun. But, that puppy may have a whole agenda of their own. It may involve activity but not with you or other dogs. They may have a tough time settling once they are wound, maybe not. Just like the puppy sitting in the corner may not be the shy one that he looks like. Many puppies who sit back and watch are highly intelligent, thinkers.
This is why it is extremely important for breeders to interact with their puppies on many different levels. Interact with and watch, watch them interact with other puppies, people, inanimate objects and on their own; how do they deal with the world around them when they don't have their posse?
Letting puppy buyers pick their own puppy is like putting a blindfold on and saying "okay, choose."