Did some side by side of the 360 and pc demos. They look pretty much identical. PC has a slight visual advantage of being a higher resolution on a smaller screen. Not enough for me to choose it specifically.
Gameplay, the control seemed to work out for me either way. Gamepad's probably the better bet. However, K&M has a huge advantage in the inventory screen. That does seem pretty minor in itself, but control pad inventory bugs me. Select slot, confirm slot, select item, confirm item. With mouse it's select slot, select item.