One reason to prefer the aluminum to the white MacBook: There is a structural problem with the white MacBook that neither older laptops nor the aluminum MacBook have. If you have cats, for instance, who are drawn to nap on the warmth of a gently glowing laptop, you will probably find some cracks around the outer edge of the panel surrounding the keyboard, where it is glued to the rest of the assembly. This is due to the pressure of the cat's weight. Any comparable weight resting on top of the closed laptop may cause this cracking.
This is not a disabling problem, but it is unsightly, and it probably admits unexpected amounts of dust into the interior of the laptop. First there is scoring about a millimeter from the edge of the panel, then small pieces of polycarbonate start to break off.
I've prevented further damage to the surface by never leaving the laptop closed on a flat surface. When the laptop is out but unattended, I always lean the LCD panel towards me at about a 45 degree angle so cats are not tempted to rest on the keyboard.