I have never trained a dog for sport. Or lived with one. I cannot elaborate on the criteria needed for such a venue.
When I was raising litters for work I was looking for the pups that best balanced a natural affinity for humans with a refusal to give up or take no for an answer. I wanted the ballsy little Hellraiser that would try anything once.
I wanted the pup that would fall off the first step and come back with a vengeance.

And do that a hundred times! I looked for the first one to climb out of the box, I liked the ones that you had to wonder if they would survive another day. I am looking for bitey, fighty little demons that seek out human companionship.
Intelligence is also a key, because an actual PPD is going to need a high level of discernment and they can't be one without the other. I like the break in the fence test. A smart pup will find it to get to you. The rest will sit there and cry.