Re: how about wives???
Well, that's a situation that I as a wife, would speak over with the hubby. Wife and hubby need to stay together on things. You can't have the mother doing all the punishing and the dad bringing home candies and toys all the time. When the kid has done something wrong, both mom and dad need to make it clear to the kid. When th kid did something great, both mom and dad need to make it clear to the kid. Easier said than done, I'm sure.
But if you're talking about general affinity...like there are some things I'll talk to my mom about because I know she understands those issues better. Some things I'll talk to my dad about because he understands better. I can't really conceive how a child would just naturally love one parent more than the other unless there was some issue with the reward punishment system.
Given that both parents are loving and caring of course. I don't know, I guess there is more to the situation than what I see at this point.