What you may not know is that many breeds today have very small populations. If some breeds were any other kind of animal they would be considered endangered. You may find it hard to believe, but breeds can become extinct. If you read any histories about dog breeds, you will find lots of references to breeds that are gone now. Countless breeds have become extinct over the centuries. In some cases we have some of their descendants because they contributed to newer breeds, but not always. Some people might not care if particular breeds become extinct, but if you are a fan of a breed, then this might matter to you. From a genetic viewpoint, it’s always good to have a wide selection of dogs that contributed to a breed’s foundation. You never know when it might be necessary to reintroduce some of the genes from an older breed for health reasons. If those breeds are extinct, that’s no longer a possibility.
Every breed can be trained to learn almost every command. However, some breeds learn a lot faster than others - making them a lot easier to train. These highly intelligent breeds pick up a command after only about five or six repetitions, they more often respond on the first time you give the command, and they remember commands even if they are not practiced often. They also learn commands even when the trainer is inexperienced and makes mistakes. So if you do not have a lot of the time to spend dog training, or you are the impatient type who gets frustrated easily, choose a breed which has a high ease of training rating.
Most all dogs will get along well with children if they are raised with them. However, some breeds have a protective streak in them and may become aggressive with children who get to close at meal time (although this should not be tolerated), or aggressive with children they have never met. These breeds will likely see the children as being underneath themselves in the "pack order" and may try to dominate them.
Some dogs will patiently put up with little children who pull their ears or accidentally poke them in the eyes, while others will not and map nip or bite back in defense. So if you want a dog who is excellent with children avoid breeds which may have a dominance streak or that have short tempers.