The understanding I got from the previews is that the girl that parents will like is less pretty than the girl Adam likes. The previews said "Will Adam choose substance over beauty". so based on that I am concluding that Adam will pick her parents choice, how would he otherwise explain to his newlyfound girlfriend that his parents didn't like her.
I am thinking that the only one who is nice and less pretty is Rachel so she will be my pick for the winner. Christine is less pretty but not nice so that wouldn't work. There is just something about that girl that rubs me the wrong way.