Product Differentiation: Is it Form or Function?

In 1896, the architect Louis Sullivan coined the phrase, form ever follows function. Does that tenet apply when differentiating products?

Is it form, an emotional reaction consumers have with a products design or aesthetics, as with cars or clothing?

Or is it function, a products purpose and performance, as with smart phones?

Here is what I would like you to do for this discussion: Take a position. What is the key to product success? Form or function? Defend and explain your position. Then select a product that supports your position and describe how its form or function differentiates it from competitive products.