Black, and it's partly because of the sleek body and the material its composed out of. I don't know to describe it in words exactly, but when you hold it in person you'll see what I mean. The iPad 1 would look better in white because it's a little more thicker and squarer, but the iPad 2 has a smooth rounded edge.
The white body would also take your eyes attention away from the screen and unto the body. It's a very loud color.
I have the white iPad 2. Bought it 6 months ago. Within a few days I put a matte/antiglare plastic protector over the screen. I love the white iPad, I've used black for I find the white far easier on the eyes. The white "border" is not distracting for me, remains very clean and it looks more modern.
I have the IPad2 in white and love it, I got a real cool case in red from Brookstone that has a built in bluetooth keyboard for when I want to type documents, it keeps the Ipad safe and takes the place of a stand since it allows the Ipad to stand up on its own while I type or while I surf the web.