I've only romanced and married Leah. I barely pay attention to Penny. So maybe I'm not the best person to ask. But there's a reason I've barely paid attention to her. She seems kind of pathetic, weak, and bland. Leah as a wife is strong, helpful, independent, thoughtful, and loving, while still maintaining her own interests. Somehow I just can't see poor little Penny - sweet as she is around kids - filling those boots.
But really, I guess it all comes down to what you think makes a good wife, doesn't it?