What side do girls go to when hugging a boy?

Straight on. Taller girls hug over the shoulders, shorter cuddle the waist.

It also depends on the situation. A greeting hug is often half-half, where both boy and girl put the right arm over the other's left shoulder and the left arm around their waist. For kissing while hugging taller girls will often put their hands on the boy's shoulders while shorter girls hug around his neck.