Percy - he gets ten out of ten in all categories.
Objectivity & open-mindedness: He's consistently objective and rational.
Debating skills: He's probably the most eloquent poster I know of - always communicates his point well.
Behaviour/attitude towards other posters: He's sometimes harsh, but only when it's well-deserved - which is usually better than being ultra-polite all the time.
Contributions to EvC: Um... he owns it. And he never fails to make a worthwhile contribution to any thread, even if it isn't serious.
Knowledge and effort: I sometimes wonder just how many degrees he has that he's not telling us about.
I don't really think there's any other choice; Percy is the first person I think of when I consider who are the best posters on EvC. If only there were more like him...
The Rock Hound
Those who fear the darkness have never seen what the light can do.