Non-flat easily takes the cake in this comparison. The shadow on the flat design is not even remotely accurate for a shadow, it makes me feel like my world is spinning. The buttons, besides actually looking clickable, make me want to click them. As far as design in general goes, it also looks like someone made the buttons worse on purpose for the non-flat version, which is why you probably like the flat version better. Why is there a black stroke? Why is the black text not the same dark blue that the rest of the layout uses? On both designs, why is the checkout button not lined up with the gray edge or the item text?

Frankly, they both look decent to me.

Non Flat looks 4% more chaotic to me . The only drawback with Flat I believe is the buttons look more like labels .