Clomid is a mixture of two isomers (different forms of the same molecule): zuclomiphene and enclomiphene. Enclomiphene is the more active isomer responsible for the testosterone-boosting effects. Zuclomiphene can have some estrogenic effects that may counteract the desired outcome.
Enclomiphene, being the pure and more active form, is generally preferred for male hypogonadism (low testosterone) as it provides more targeted action with potentially fewer side effects.