When I got Esme, I knew I wanted a medium sized yorkie, not too big, not a tiny and I knew I wanted a female. That left me with two to choose from. Then I looked at their faces and how they were behaving with the other puppies. I picked Esme because she had a very sweet face AND because the other dog was biting the other puppies!
Which is ironic, because Esme has turned out to be a biter! I think the above poster had some great suggestions!