"Pick of the Litter" is one of those terms that people who are interested in dogs run into sooner or later. Those with some expertise probably know that it means "first choice" whereas the layman seems to assume that it means "the best puppy."
Is there a difference? Sure! If someone is intent on picking a dog based primarily on conformation, in the hopes of selecting a future breed champion, then "best" means one thing. But, if you're planning on doing obedience, then physical construction may well take second place to the amount of eye contact a puppy makes.
Whereas, in selecting a dog for obedience purposes, your Pick of the Litter means you want a "willing-to-please" attitude, if you're selecting a dog with racing or go-to-ground potential, you may look for the puppy who seems most adventuresome and independent as Pick of the Litter. For a family pet, the "best" or "pick" may be the one who is most laid back or the one who likes to snuggle with the kids.
Others may believe that pick of the Litter is the "Biggest and heavier one" no matter what the standard of the breed calls upon. The Term "PICK OF THE LITTER" is extremely ample and it has completely different meanings to every person.
I can have a litter with 5 Picks Of The Litter, each one in different venues! Each one surpasses the other in different attributes, Personalities, temperament, conformation, attitudes and still each one is the Pick of the Litter in their own characteristics and Personalities.
There are dogs who seem to have it all. The versatile ones with brains, beauty and the kind of personality that seems to adjust to any situation. But often, dogs that excel in one area may come up short in another. (Not unlike people!) So, if you're ever offered "pick of the litter," the first thing to do is define what attributes are important to you, and then go ahead and pick the puppy that you think is "best."