Depends on what kind of hunting dog. I agree with Katie that pedigree says a lot.
If you are going to use the dog to retrieve, then you really want to see which puppy pays attention to you (it’s a pretty good indicator for intelligence too).
If you want a pointer, then look for the traits of a pointer, the stance, the tail, pausing rather than going headlong into a puppy brawl.
If you want a chaser (as in fox, coon, rabbit etc), then look for that unwavering single minded fixation on a toy and dominance.
But really, you can train most labs (pedigreed or otherwise) to be pretty good hunting partners regardless of the traits. Those are just traits that make dogs that are great hunters (and competition winners).