Grothmar Wardowns is where I farmed, there's a Siege Devourer right across the bridge to the east you can use to make things a lot faster. After you clear the area you can go into Dalada Uplands for more cannonfodder, or you can just farm in Dalada in general; it has more enemies and if I remember correctly there are about 150 enemies if you go around the edges of the area alone.
If you farm with another player you should get two Siege Devourers to completely splatter everything.
Do all the dungeons before farming, they give out good faction point rewards and then you can also give them the completed book to get an extra 2500 points.