ESO again is a solid contender for some of the best pvp battles I've ever seen in an MMO. Hundreds of players at any one time duking it out. Siege battles galore. While they do have your typical pvp death match modes, the open world scale full on battle assaults with literally an endless time limit is near second to none.
Zero risk/zero award instance PvP. I don't even consider a game that doesn't have open world PvP a PvP game.