it's a tough one. i got chinchi from a pet store and he never had any health problems apart from hard skin on his feet (i totally panicked over that). sadly he died when he was just three as the chin i got from a breeder that was supposed to be a boy turned out to be a girl but we only found out when she gave birth. so chinchi had to be neutered and developed complications
this obviously would not have happened had he not had the surgery. he was a pink white and weighed over 800g which is big for a boy, he had fantastic fur quality and was generally a very healthy happy chin.
fluffy i got from a breeder. i live on the isle of man and there's a breeder who owns a pet shop, he only has one breeding pair so not many litters but he goes away and brings animals from breeders from the uk. he brought fluffy for me and a/ she was supposed to be a boy b/ she just had a dental and a lot of her back teeth are growing at an angle.
i think that there are quality breeders and there are breeders who don't necessarily know the history of the breeding pair far enough etc. so i would say quality breeder is probably your best choice. other breeders and pet shops perhaps both are hit and miss. however you decided, i would strongly suggest you have the sexes triple checked. i bought chinchi as a girl, he was a boy. fluffy was supposed to be a boy, she's a girl.