Which dog is right for you.. size
So you've decided you want a dog.. you have figured out sorta the temperament you think you want, but you know to discuss that more with your reputable breeder. So now.. Health is factor.
Some breeds are prone to hereditary diseases or conditions more so than other breeds. Many can be screened for, such as hip or eye problems. Such certifications should be made available to you when you are thinking about a puppy. The reputable breeder is usually proud to produce these papers. If the breeder says "vet check has been done" that is not sufficient. CREF certification for eye's is one certification that can be done on the parents. OFFA.org will have the records of the hip certifications. If the breeder had them done, if they are not on-line or they can not produce a copy of the certifications that should be a clue they are not reputable and could be a puppy mill or back yard breeder.
When the parents of the puppy are tested thru proper channels (more than a vet check) this gives you an idea of what your puppy is getting from each parent. Each breed has it's own sets of health issues that they watch for. So when you decide on the breed look up the parent club and see what they recommend that the parents have tested. Then work with your reputable breeder to learn more about the health issues that breed has and make sure your prepared to care for these needs. If you think you can not handle it, then don't go further with the breed. It's OK. Reputable breeders would rather you learn about things and decide this is not for you, then for you to be ignorant and get a puppy and then dump their puppy in a shelter later on because you didn't understand. Often if you think you like breed a, and you talk to a reputable breeder and find out this is not the breed for you, the breeder will not be offended and may even offer a suggestion of a breed that would work. And often they have a friend or know another person in that breed they can recommend. Health issues are very important and research should be done.