My vote goes out for PC, but only because I have more experience with them. As I understand it, Microsoft does better interface, but Apple pwns at aesthetics. Hence, the sleek iPod and the ugly, yet versatile Zune. I suspect that this is because if someone made a device that was both attractive and chock full of accesible power, the world would end.
...Wait... *remembers iPhone* NOOOOOOOOO!!! *universe blows up*