I want to know a good pvp server with a good balance of Horde and Alliance

I would say gorfiend for horde idk about alliance

Come to Auchindoun!!

Good balance of Horde vs Alliance.
We have a low population but it's growing fast.
and You can make good money on our AH.  'cause there's plenty of resources avaible.  You won't have to fight for them.

Kel Thuzad

Bonechewer is decent. Sometimes tough to find a group though.

Bloodfurnace has a great group for horde.  I have not tried alliance so can't speak for them.  Good mix of gear and ingredients on AH and lots of friendly guilds. 

Good luck,
Tec

Azshara!!!!!!!!!!!!!!!!!!!

I'm liking Darkspear just fine as a horde player. Seems like quite a lot of players on both sides and city raids go both directions. It's a medium to heavy population server, so the economy is good and finding weapons and gear on the AH for cheap at low levels is relatively easy.