PoP Leveling Guide - Plane of Justice
This is the first and easiest area of Plane of Justice. Most lower level groups hang out where you see the green arrow on the map, by the Plane of Tranquility zone out. You can pull the mobs that wander the halls (watch out they are all social with each other) as well as the mobs out of the jails on the first floor.
I recommend you stay in the upper portion of PoJ until you're 60+ and with a group equally as strong or more powerful. It's much harder to find a "safe" area to pull too downstairs and a majority of the mobs in this zone are social with one another and will agro if you attack their friends.
Once you're higher level and you can handle the harder parts of Plane of Justice, the tunnels you see on the map above as well as the green area offer a great hunting location.
12/1/17 - If you're really familiar with the lower floors please leave me a comment below with any information about them, I don't know much about them but I will hopefully have time to hunt there sooner or later to learn a little.