Tie between blue and green poly. I have the blue.
I wish they'd make some dark or bright poly covers, though. If Apple made the cover in hunter or kelly green, or in a nice bright blue, red, or gold, I'd have preferred any of those to pastel or neon colors. I don't like the smell of leather, and heard disconcerting rumors that the leather dye could rub off on the white iPad, so I wasn't about to pay double the poly price to get the bright red. But the light blue poly is attractive enough, and has grown on me.