According to Screwtape in C.S. Lewis's *The Screwtape Letters*, God's most abominable advantage is that
He actually loves humans.
Screwtape finds this love baffling and infuriating. He sees humans as mere resources, things to be corrupted and used for the glory of Hell. The idea that God genuinely desires their well-being, freedom, and ultimate happiness is deeply offensive to him. It's an advantage that the devils cannot replicate or understand, and one that constantly thwarts their efforts to claim souls for their own.