I think action is better than words. Stick your dad on a mac for a week or so and make him go back to PC. If that doesn't convince him, sick a virus on the PC, not a harmful one though

I would say 13" is probably better for an average student. You get the mobility and all the power you need for school work. But if your going into media design and video editing, get the 15" for the power. Besides, MacBook Pros are really nicely designed the 15" isn't that much heavier and hasslesome than the 13".