Bud size does not dictate quality and it certainly does not dictate if you will get a clear soaring head high or if you will get a couch-lock body stone.
High THC content is a key part of quality and to have that you need to let your plants ripen, you need to let them mature. Even high THC content alone does not guarantee quality.
It takes the proper mix/blend of various, or all, cannabinoids in the trichome heads for true quality and true potency and that is manily dependent on genetics and then on the conditions the plants were grown in and it of course also depends on plant maturity when harvested and then it depends on a properly performed slow dry in proper conditions and a properly done slow cure.