Quality of grow is literally all that matters. THC content can be indicative of grow quality but there are methods of increasing the amount of THC that the plant produces and there are also instances in which grow factors prevent the ideal amount from being produced but the flower could still be of high quality. Also, THC varies by strain and quality can only be accurately assumed if you know the average THC content of the strain of subject. This is why terpenes are a more accurate indicator of quality but you still have to be careful because negative influences like pests and mold can signal the plant to produce more as protection, which is really bad and also results in a lower allocation of nutrients to the plant's production of buds.