My advice would be to look for breeders and strains that OTHER breeders use in their own breeding. I'm into Bodhi seeds for instance... the number of other breeders who use his stuff is growing like wildfire. Just off the top of my head, without endorsing any in particular, you see many crosses made with genes from companies like Brothers Grimm, Subcool, Crockett Farms, Serious Seeds, Exotic Genetix. What you don't see are many breeders using Barney's Farm or mysterious Spanish companies. You can get fantastic plants from them for sure but it's all about the odds... how many stinkers are you going to have to go through before you find a true queen. You're going to spend 4 months to find out if they're any good or not. Time and real estate are precious.
And then, before you make a purchase, search through the forums for other people's experience with those seeds. If you're ready to dig deeper, there are many smaller "boutique" breeders that are considered by their fans to be even better than most of the big companies... look for names that get boundless love in the forums. It's tough to negotiate all the noise for sure... just try to make a well educated guess.