Good grief, they're ALL so cute!
Do you want a purebred puppy or a mixed breed (nowadays called "Designer Dogs")?
Choosing the breeder and the puppy will be exactly the same!
An experienced and knowlegeable breeder will want the puppy placed in the home most suited to its personality. The breeder will not want this puppy to go to just any home. If the breeder seems very anxious for you to take the puppy, look elsewhere. If, on the other hand, you feel grilled by this breeder, (s)he has the pup's welfare foremost in mind, and you know that from whelping to this point, the pup has had a carefully orchestrated experience in the world. This is very important. What does this tell you about pet stores and flea markets???
Observing the Litter
I first watch the puppy relate to it's littermates. Depending on the projected future of this pup, I want either a dominant, independent pup (working dog prospect) or a middle-of-the-road pup (pet prospect). Under no circumstances do I want a timid, wallflower underdog. I want to give myself every advantage in raising a pup into the dog I want, and there is no reason to deliberately start out with a handicap! Go ahead and rescue this poor thing if you wish, but go in knowing your life is going to get way more complicated from here.
Wait a second...this is how I make my living...fixing the mistakes...perhaps I should reconsider my advice!
Testing the Puppy
I want to see confidence--does the pup come right up to greet me? (Is the world a nice place?)
I look for a cooperative nature--will he go see what I threw and bring it back for me to play with? (Has he learned that people are fun?)
I check for easy bonding (good in a puppy, not good in a teenaged daughter)--if I walk away, does the puppy follow me?
I test for boldness--does the puppy want to see what made that noise, or does he run way from it?
The right dog for me starts out and grows up with that look in his eye that says, "I'm not sure what's going on, but I bet it will be fun!"
Puppy testing criteria are in many books. One of my favorites is "How to Raise a Puppy You Can Live With" by Rutherford and Neill. It is available in paperback, and most libraries keep several copies on the shelves.
Housebreaking is what needs to be done for the humans, not the puppy. An "accident" in the house is the human accident--obviously the puppy needed to relieve himself, and was not outside to do it. The pup's habits are formed by repetition. If the puppy is outside when he needs to relieve himself, that is where he will decide is the best place to go. So commit to having the puppy under your constant surveilance or crated the first few weeks. After a few days of being taken out to potty, the puppy will realize the door is the portal to outside. If at any time, he looks at the door or sits near the door, take the little guy out. Soon he will add a signal--a whine or a scratch--he is trying to train you, so show him how smart you are--respond immediately to his signal. After awhile, as his control gets stronger, he will be patient for you to come let him out. Don't let him down.
Early on, a puppy will have to potty 15-20 minutes after eating solid food, and soon after drinking. He also will need to go out if he has just waken up (don't you?), and after he has been playing. Get him into the habit of being outside when he relieves himself, and you will be surprised how quickly your dog has housebroken you.
In a family with multiple dogs, the other dogs make quick work of housebreaking through example.