Guild Wars has by far the best PvP system I've seen in a MMO, but I haven't played WAR, and I heard Warhammer has very good PvP.
WoW will never have balanced PvP because they try to balance classes around PvE -and- PvP, which simply doesn't work, especially when it comes to bursty damage and crowd control.
GW's PvP system has a few notable changes - first off, you can actually spectate matches, record demos of these matches, watch them later, etc, etc. Something WoW should have had for Arena. Secondly, instead of talent specs changing the way a class is played, you can only take 6 abilities into combat at once, so in a PvP match, you can only choose 6 - so you need to balance offensive, defensive, and support skills, so it's not like you could have a warlock who can skillcoil, chaos bolt/incinerate you for 18k, and then STILL be able to use his demonic circle teleport, and have a spell-locking pet, and still have powerful DoTs.
You'd have to balance between there instead, so no class is really overpowered, per se, but instead the game relies more on teamwork.
Also, if you don't want to PvE, you don't have to, you can roll a character at level 20 that can do nothing but PvP, and it will do nothing but PvP.
WAR on the other hand, from a friend of mine who plays, I know the game actually has COLLISION DETECTION, so melee can actually form a wall to block enemy players from getting to ranged, high-ground has obvious advantages, choke points are actually helpful instead of classes running through you, etc...And it has much less control abilities - less stuns, less incapacitates, etc. So you won't have an arena match where a druid can chain-cyclone you several times and then you can be chain-polymorphed as well, and if you trinket one, their partner gets back to CC you within the few seconds you had to move freely. It's more like you're actually able to use your abilities instead of other characters taking them away from you.
Now, neither system is perfect, or if you're looking for a competitive edge, "good," but compared to WoW, they're much better for that kind of PvP.