Which creatures from the alternative upgrade options do you choose?

This ability is too unpredictable... and it fails too often. Sometimes you get lucky, but I lost all my shamans in a similar situation... while trappers only lose initiative.

Well, if you manage to gather a relatively large number of goblins, why not take shamans? If the enemy has a mage, the battle will likely take place on their side anyway (meaning there's no one to set traps on), and goblin warriors aren't that great, so they might as well try their luck with magic disruption. After all, a single disrupted spell like "Control Animal," "Earth Shock," or "Phoenix" can decide the outcome of a battle when the forces are evenly matched... IMHO.