Demon temple is the fastest, they give the most silver and they spawn like blazes. Set a rune on top of the temple near the penagram and start kicking them around. Keep in mind that the faction creature you can spawn does NOT include the creature your faction is aligned with, so when you sign up for SL don't plan on farming demons, for TB you can't farm serpents, for council of mages no wisps, and for Minax no ogre lords.