If the secondary hero also happens to have the Leadership skill (or if it's Cyra), then it's almost always necessary to upgrade that hero's troop recruitment skill.
As a result, troop recruitment + the sacrificial pit will give you +3 Assassins, +3 Furies, and +1 Minotaur.
I like to choose Ianna, and in her army, even +1 Fury per week is a big bonus. In the process, it's quite likely that you'll be able to throw some other joined neutral creatures into the pit.