Most popular EU realms for PvP? (retail)

My toons (mixed Horde/Alliance) are stuck on a dead server cluster, so I'm looking to transfer them. Which realms have active PvP players/guilds/communities?

I see a lot of Horde players from Kazzak/Stormscale and a lot of Alliance players from Ravencrest, but not sure where the "place to be" is.