Oh man, that is a great question.
The best PVP classes are PPU (duh), APU (best damage with holy frost and anti-buff), WoC rifle spy with AK, aaaaandd everyone else is kinda shit? WoC pistols spys are fine, WoC pistol PEs are OK, Slasher PEs are fine. Did I miss anything? Probably, but the game still desperately needs a rare rebalance (come on Zoltan!!!)
OP fights are fun, but I'm not that into Spys running so fucking fast I cant hit them (redflash and paratemol x-forte). We need more viable rares and less required classes (ppu, apu) and we need to nerf stealth. Stealth whoring is a pain in the ass and it's a huge part of current pvp. True Sight Sanctum isn't enough to combat stealth and we need more options.
I love PVP, it's why I play NC, but since I still have PVE goals and new character ideas, I'm still busy leveling new characters and trying new builds. Yeah I PVP on Run, Jack Drake, My Ppu, and others, but I'm not happy with them or their style quite yet. There are not many viable ways to play NC and win OP wars right now, which sucks, because I hate choosing cookie-cutter play-styles
edit: I forgot to mention: Everyone has 2 or more accounts and they all dual log. If you kill one guy, he'll log his alt and show up. So you're fighting 4 dudes but it feels like 8-12 dudes. I miss Pluto :\