Seedboutique has some reputable breeders and strains. Same with their sister site Seedbay. Attitude is good too, but you get more freebies from Seedbay and Boutique.

Some of the better breeders there are:
B.O.G.
Connoisseur Genetics
DJ Shorts
Dutchgrown Seeds
Head Seeds (when they are actually available)
Mandala Seeds
Mosca Negra
Mr. Nice Seeds (mrnice.nl might have some more strains, can't go wrong with these guys. Their Black Widow is the original White Widow, legendary)
Nirvana
Reservoir
Serious Seeds

They are all pretty good, but those seem to be the most popular. Greenhouse has some mixed reviews, but I was happy with my purchase.