[Messianic]

If you don't care about your qeynos faction, you can do 4 guards in NK (two on bridge to SK, two in tower next to gypsy camp) until 42 (they lblue out then). Very stable, they never resist, no social aggro because there are only 5 mobs in the area on the faction (guard fredrick inside the tower ignores the ones on the bridge if you pull them first and from the side of the bridge). They usually repop right when you've medded enough mana for another quad.

It's also right next to a port location ($$).