Every parent defines the lucky child differently: for some the choice is based on beauty, for others brains, for others birth order. Once the selection is made, extra attention and other goodies are subtly steered that child’s way, even if parents don’t realize they’re doing it.
via TIME: Playing Favorites: Why Mom Likes You (or One of Your Siblings) Best
Update (October 7, 2011): Due to the recent death of Apple’s founder, Steve Jobs, they changed the TIME Magazine cover for their next issue. The shown image here is originally the next cover for TIME’s latest issue.
Br. Allen 
As a parent, all I can say is that this is embarrassingly true.
Hey! I just saw this in National Bookstore! :p and yeah parents will have favoritism even if they would not like to admit it. I am sure once we become parents, we would have our “preferred child” too.