How do you pick your pups

If I get one off someone's else's yard I just get one it really don't matter to me. But the last litter of pups I had I kept all of them and when they was six weeks old I picked out one I like and would of got if it was coming off another yard. I kept all but picked my picks to see if I picked the best or not. Well the one I picked died and the one I didn't like none is looking like going to be the best pup. So it's really like rolling the dice when getting a pup. I think keeping the whole litter is the way to go then pick a couple pups later in life to keep that way you don't end up getting rid of the best ones