I got Elsa at 9.5 weeks old. She was a bit old to check temperament properly like most candidates, but somehow I lucked out on my pick.
We (My SO and I) went to meet her and her 9 siblings out in the country. Nick picked his girl (Britta) out when she ran up and played with him. Her tail was up high, was very energetic, and played with the other pups a lot. She was cute, but the alpha cues I was getting from her were too strong for my interest.
I picked my baby out when I saw her interacting, but not overly interested with the other puppies. She obviously had energy, but wasn't attached to the others like Britta seemed to be. She ran around and played, but was willing for me to pick her up and submitted when I did. She didn't seem nervous about things around her, she was interested in me but not for too long, and she was SO SOFT! Okay, so, I was trying really hard to pay attention to temperament, but her fur just sealed the deal over the two others I was watching.
So far, she has worked out well. She has higher energy than I originally expected and isn't as focused as I would have liked, but she has done everything I've asked and put up with a lot of goofy messups on my part. She is still turning out great and I'm thrilled with her progress.