breeder rats are much more socialized, although i think most everyone here has agreed that petco rats are still better than petsmart rats. they are also properly sexed, which is sometimes the problem when rats are stuffed in a bin together, and you might end up with a pregnant female from a petstore. happened with a hamster of mine, and several people here have gotten rat litters that way. also, breeder rats tend to be healthier since they are not exposed to the overcrowded conditions of binned rats at petstores. many petstores also do not feed a proper rat diet or keep their rats on proper rat bedding, further adding to potential health problems. many petstores (i think definitely petsmart more than petco here) also get their rats from people who just breed rats for rats, and not for health and temperament, like breeders do, and you can end up with an anti-social rat that develops many tumors and has respiratory issues due to genetics. by getting a rat from an accredited breeder, you can help to reduce the amount of profit that those people make, and in the end, you'll have a better rat for a longer amount of time!
on that note, both my girls were from petstores, and admittedly, picasso had some sneezing and head-shaking when i first got her from petco. mozart was from a smaller store that bred their rats one litter at a time in aquariums, but has had no health problems to date. i was going to get picasso's friend from a litter, but i totally understand where you're coming from on how hard it is to get a rat from a breeder sometimes. one breeder didn't want to adopt to me because she thought i was someone famous, so i don't even know what the **** happened there...
ultimately it's up to you, but get a rat from a breeder if it's at all possible.