Based on my experience with the Psion S5, I reckon a thinner front edge would help with typing, meaning you could stretch your thumbs to reach awkward combinations futher, more easily without the corner digging into your palm. Of course, the S5 achieved this by being a much simpler device and employing a sliding keyboard hinge that would be stupidly expensive to copy, and probably patented to the hilt already. But still, that's why I'd like the base unit, at least at the front to be thinner.
I also think a little could be saved from the top already if the keyboard and game buttons could be made flatter, so the lip around the top part could be shrunk and make the unit look a little more classy.
So top thinner for aesthetic reasons, bottom thinner for comfort. But it's a big ask for a potential device with so much packed in, and to be honest I can more than live with the Pandora case as is.