Piggy. No offense, but here's my reasoning. Guillame wants to absorb Enweil and create an empire.
The Lord of the Flies is another name for Beelzebub one of the 7 Princes of Hell in the Christian Mythos. He represents the sin of Gluttony, and until the fat kid - the glutton - was killed, they were haunted by the influence of a Prince of Hell.
... I had way too much free time at work last summer...