Why do Fathers Love their Daughters More & Mothers their Sons?

It's natural for men to compete with each other, but it's usually healthy competition. Boys look up to their fathers, but also compete with them as the alpha-male of the household. This is a natural and subconscious response. Boys feel less threatened by their mothers and so are more apt to share more with their mothers, especially in the area of feelings. This makes mothers and Sons closer than Fathers and Sons. The same goes with bringing Fathers and Daughters closer together

According to Freud, children go through a phase of attachments to the opposite sex parent which is called "oedipal complex", based on the ancient Greek story of Oedipus who ended up unknowingly killing his father and marrying his mother.
Basically the little boy is "in love" with his mommy until he realizes that daddy won't let him take her away so the boy redirects his desire from his mom to other women.

This theory was very rough then and has been refined and reviewed almost beyond recognition many times. But yeah girls do go through a phase where daddy's the best man in the world and boys through a phase where mommy's the most beautiful.

In the early days of psychology, Sigmund Freud developed a unique conception of how the child’s personality develops.

Freud theorized that child development occurs in three distinct phases: the oral stage, the anal stage and the phallic stage. The Oedipus and Electra complexes occur at a subconscious level within boys and girls respectively, during the phallic stage of development.

The Oedipus Complex

The Oedipus complex argues that the young boy desires his mother as a love interest. According to Freud, "Unfortunately for the boy, his father stands in the way of his love. The boy therefore feels aggression and envy towards this rival, his father, and also feels fear that the father will strike back at him." The boy expects that he will punished by his father, for his desire, by being castrated.

This anxiety is exacerbated when the boy realizes that girls have no penis; he assumes that they have had their penis removed as a punishment. The boy realizes that he cannot possess his mother and place himself opposite his father as a rival; instead he learns that he must possess another female and identify with his father.

The Electra Complex

The Electra complex acts as the female equivalent of the Oedipus complex states that the young girl is attached to the mother, like the young boy. This is not surprising, as the mother tends to be the primary caregiver and object of desire.

Upon realizing that the she, as all women, has no penis and subsequently she suffers "penis envy." Like the boy in the Oedipus complex, "the girl learns her role by identifying with her mother in an attempt to possess her father vicariously."

Fixation in Freud's Child Development Theory

As with the other stages in the child’s development, fixation that occurs at the phallic stage may produce certain characteristics, in this case: "a phallic character, who is reckless, resolute, self-assured, and narcissistic – excessively vain and proud." The failure to resolve the conflict can also cause a person to be afraid or incapable of close love.

Freud postulated that fixation at the phallic stage could be a root cause of homosexuality.

Today's View of the Oedipus and Electra Complex

Although both the Oedipus and Electra complexes have been subjected to harsh criticism, especially from feminists, Freud’s influence does seem to echo throughout adult life in terms of male and female characteristics and behaviors.

Boys learn that they must become like their father, who is stereotypically aggressive, ambitious, powerful, and in direct contrast to his mother, who is stereotypically passive, obedient and nurturing.

As the boy learns to identify with his father, the girl learns to identify with the mother. As such, the way that both the boy and the girl come to relate to their mother and father, by way of the Oedipus and Electra complexes, will determine their behaviors and affect their relationships in later life.