Very cool thread, I am not a parent, I am interested to hear what parents say.
I'm the oldest and always assumed I was the favorite, at least my Mom's, then I happened to see a note she'd written to my sister, and it had kind of a different tone than the way she talks to me, more intimate, that I realized maybe I'm not the favorite.
Plus my sister went to college, got married, had good jobs, and never worried my folks, so I would understand if she's their favorite.