Hazard is still very young, has seemingly taken to English football like a duck to water and will bang in a shitload of goals while racking up loads of assists. The guy has one hell of a future ahead of him, that's for certain.
... and yet I still say De Rossi. As great as Hazard is, we don't need that type of player right now. De Rossi on the other hand is a perfect fit for the way we play, an improvement on what we already have and would walk straight into the team.