I probably sound like an idiot, but does using the screen on the highest brightness setting decrease the life of the panel over the years? Just wondering, I do have AppleCare to back me up.
The 17" over time would definately loose brightness.
The 15" will be as bright as the day you bought it until the LEDs bite it. Which is to sa the MBP will be in a recycling bin by that point for its obsolesence....