We've had GSDs since 1986, and are on #4 & #5 together - every single one of them has picked a "special" person between the two of us. For all of our females (4), my husband has been that person. Keefer, our only male, is totally, 100% my
dog. But he also adores Tom, and Tom adores him. It's just that Keef is my shadow, he always knows where I am and what I'm doing because he keeps me constantly in sight. If I leave a room, he follows. Always.
I do all the feeding, grooming, vet visits, and training, so it's certainly not about that. Halo loves me too, she seeks me out for affection frequently, and we race in flyball together so she works very well for me, but if she had to choose between us, she'd chose him. Total Daddy's girl.