Green looks better, sounds better
K&N *MUCH* better fit, comes with cold air feeds (Green doesnt), better build quality.
According to the performance reviews, K&N slightly more BHP, but imo nothing in it - both gave good performance improvements.
I had both, i've ran both for over a week. Like Stu says, personal preference. I stuck with the K&N in the end, mainly because I liked the sticker

:P