Picking a Puppy

Although I still have a long wait before I can get a dog, I was wondering if there is anything specific I should do when I go to pick my puppy. I already found a breeder with policies I agree with, so that part is done, but when the litter is born and I go meet them once they've grown up a little, are there any little tests I can do to help pick which puppy would fit me best?

I want to play in the various dog sports, especially agility. I'd like to be somewhat competitive (as in I'd like to compete and win titles ventually, but I'm more concerned with my dog having fun and enjoying himself). So what little tests did you use when you've picked out puppies? (especially agility prospects!)

It is my understanding that "generally" the breeder picks which puppy goes to which home.

IMO, the breeder should ultimately be the one matching you to the right puppy in the litter. No one knows each puppy's in-n-outs like the breeder, who raised them, does. As well, some breeders will also do thorough evaluations of all the puppies in a litter with friends/other breeders who will also give their opinions on each puppy as they evaluate them. But in the end, it is far better this way.

My last breeder dog was picked by the breeder for me, she did give me the option of taking the other bitch puppy who was left if I wanted, she overall had good quality to her too, but the breeder said the puppy she picked out had a better personality for what I was looking into, and her conformation is excellent.