Is he able, but not willing? Then he is malevolent.
Is he both able and willing. Then Whence Cometh Evil?
Is he neither able nor willing? Then why call him God?"
The problem with this objection is that it assumes there are only two factors to consider. But if we add a third proposition, say that God may allow evil to exist temporarily for a higher purpose, then the argument simply crumbles.
For fun, I've thought about reformulating the argument and turning it on its head. It would go something like this:
Atheists claim that Epicurus' Riddle is powerful enough to topple belief in God for rational people.
Yet rational people still believe in God.
So, why appeal to Epicurus' Riddle?