For a lioness, for example, the safest bet would be to have a girl. Even if her daughter isn’t the strongest or highest-ranking female, she will most likely have at least the average number of cubs.
Sons, on the other hand, are a high-risk but potentially high-reward bet. Most male lions don’t reproduce because they are beat out by the few alpha males that father the vast majority of cubs. With sons, she could end up with zero grandcubs, or hit the genetic jackpot.