Fem are theoretically better, because the breeder can see the female flower traits carried by both parents. Both parents should be fire. Whereas with regs male selection is dubious at best. Lots of stem rubbing and virtually zero male selection from comparing progeny.
In practice it depends on the breeder and the genetics they are using. I'll always choose, for example, Professor P of Dynasty's regs over bulk fem trash from dishonest businesses just trying to make a buck. However, there are tons of good fem breeders now and even some old school reg breeders are going fem only, like Mr Soul. Look for real stoners who have a passion for Cannabis.