I've heard different recommendations on how to pick a puppy from a litter to fit a person's needs/lifestyle. I've heard that if I live an active lifestyle, then I should pick the one that runs up to me first, because that one is going to be the friendliest, and easiest to train.
On the other hand, I've also heard not to pick that one, because it will have the most energy, and therefore harder to train. So if I don't live a very active lifestyle, or if I have children, then I should pick the one in the back instead, because it will be the gentlest and calmest.
But, I've heard that the one in the back is also a bad choice, because it's more likely to have problems socializing.
I've always gone by look (a bit shallow I know), but is there really a way you can tell from a litter of puppies how they'll be for the rest of their lives? Is there any truth to these guidelines?