GW2 has the RvR maps that works like a charm.

A tri-faction PvP, that could lead to a "Maelstrom vs Gridania vs Uld'ah" fight, on a gigantic map where people can join/leave anytime.
You can build/destroy, attack/defend.
Playing in small group or a big one.

It is what make the game attractive, as you can engage in fun instantly.
It also gives buffs has your server (nation here) gain some ressource (with no penalties if you loose ressource or fall down behind the others servers).


This is a(n almost) non-toxic way of playing PvP as it makes PvE players enjoying PvP in large group.