Don't do the magic guild. A lot of people actually bot ranged there, and you're taking up their monsters so you are liable to being reported. Also, a LOT of people bot magic there as well.
A few caged monsters that I always like to torment are the Lesser in the Wizard's Tower, all of the Sarim Jail monsters, the Chaos Druid in Varrock Castle, and the Greater Demons in the Watchtower Dungeon. Another favorite (non-caged) monster are shooting the zombies across the sewer stream in the Varrock Sewers Dungeon.