The popular redhead models are amazing in VNs, like that one with the redhead that has the part off to the side is amazing in just about every version of her that I see. If she has black hair, then tattoos and goth, blonde and brunette are pretty varied.
Brunettes, blondes, redheads or bald, the key, for me, is in the subtle details such as: A sweet expression, a shy look or big boobs. Yes, big boobs definitely help a lot.