For all those new players wondering which server to choose for coming back to KO, dont think too much, just go for PIANA!
It has english players on both sides and you don't need +9-10s to do good in pk, even +7's is fine if you got skills u gonna own!
Anyway, I got a lvl 81 character which I geared up for CZ and I can say from daily observations that CZ is quite active, especially during evenings (turk time).
Then I decided to make an ardream character and see how it goes...i sold all my lvl 81 items to hook up my ardream one. Trust me... Ardream is really active, sometimes its 100x humans vs 50-60 orcs. PK is great... the only thing that sux a lil is that there is no DD helmets on server and 90% of ardream is sins. Still pk is really good! go for it !