Dante, hands down.
Kratos became the God of War because he defeated Ares, and that was solely because he had opened Pandora's Box and used its inner power. Otherwise, he wouldn't have stood a ghost of a chance. Having taken his place in Ares' throne, he had regained the Blades of Chaos and become the new God of War.
Now Dante, he's completely different. He may be a man-sized half demon, an insect compared to Kratos, but I believe he's way more powerful. Let's look at his credentials. He's defeated Mundus, Argosax, his brother, Despair Embodied, hell, even a manifestation of his father's power. Kratos may have killed a god, and become one himself, but Dante's almost single-handedly eliminated so many all-powerful demons in his time, even Zeus would have reason to worry if Dante ascended Mount Olympus with Rebellion in his hand.
If you think about it, Dante is the more powerful of the two.