The reason for Filipinos being first choice is that I understand that the majority are quite devout Catholics, so they would follow the guidance clearly described below. I definitely think the best people to enslave might have to be Christian. Buddhists are no good, because they just think they will be reincarnated so this life doesn't matter and Muslims are out because they don't eat bacon.

Slaves, obey your earthly masters with deep respect and fear. Serve them sincerely as you would serve Christ. Ephesians 6:5 NLT