To be perfectly honest, I would want the breeder to choose for me. In general, a good breeder will spend many, many hours observing those puppies and (since hopefully she is keeping one for herself) will be making careful notes on the different personality traits and things she notices. Most breeders don't make that decision until close to the 7th/8th week, so I'm surprised they're letting you pick your own puppy at 6 weeks.
Whatever pup you bring home, they are all individuals and the time and effort you put into training and developing the relationship with him or her for the first year or two of life together will develop that bond. You really do get out what you put in. Find an obedience class to sign up for with your new baby and take her everywhere with you that you can, running errands, out to public places etc. THe more time she spends out with you the more fun she will tend to be. Best of luck