Which realm to do only PvP ?

Hi.

I'm new here and I wonder...what's the perfect realm to do only PvP ?
I know there's Blackrock for that (instant 80) but I was thinking that maybe there are more people doing PvP on Deathwing/Ragnaros than Blackrock.

Thanks and have a nice day =)

check the PvP ladder and judge which one is more active: http://armory.warmane.com/
keep in mind that:
1) Deathwing-Ragnaros are going to be merged so there will be 1 realm with around 7k-8k ppl I guess
2) do not get confused by numbers because:
---a) blackrock= only players doing Duel- Bgs- Arena
---b) deathwings-ragnaros= players doing Duel -Bgs - Arenas and.... Levelling- Dungeon/Raids- Skilling Profession-Farming Gold-having fun in /g or any guild voice chat
3) if you decided to play on Blackrock doesnt mean you CAN'T start playing Deathwing-Ragnaros too, because on Blackrock you will be full geared from the beginning so after doing some bgs/arenas you can log on the other realms

Thanks for your answer.
I will probably go on Blackrock and do some quests on Deathwing sometimes.