There are many top quality breeders out there, I always order off of pickandmixseeds never had a problem. I usually tend to go with white label, sensiseeds, greenhouse and barneys farm. Beware of what strains you choose, I tend to go for well known tried and tested strains. Just because a seed bank is better known does not mean all of their genetics will be good, just like breeders that have not got a good reputation may have a strain better than any of the mentioned above. A lot of this comes down to the way that you grow, you can grow an inferior strain to a better quality than the superior strain.
Someone that does not have a clue will buy a strain grow it poorly and then complain that the genetics were not of any use or get a turn out that they are happy with having never seen any other plants from start to finish and tell everyone how there rubbish genetics are good.
If you want to be safe buy a tried and tested strain but make sure you read a lot of reviews and see a lot of pictures of it first, if you want to try and find the perfect strain for you buy lots of different strains from all sort of breeders except (nirvana lol) but be a bit more vigilant be aware that your plants may turn hemaphrodite and your crop will be reduced in mass. I enjoy a good mix at times in the hunt for a tasty powerful strain I grew 13 different strains in a 1.2m tent.
Perfect example of why you should read a lot of reviews is this thread, people advising nirvana, nirvanas seeds are poor the description of the strains clearly lie never mind the plants thereself.