You don't know too much of Courtois abilities. Courtois' presence in the box with Atleti is far greater than De Gea's at Atleti. Even when you compare him to De Gea from now it's not one sided on who has the better presence in the box. Also, De Gea is rather skinny and nimble. Not the perfect fit for the EPL and that is why it took him a while to adapt. Courtois is tall and stronger than De Gea. Plus, despite his height, he is extremely agile. He is going to fit right in immidiately. Just like Van Der Sar and Petr Cech.
It is best to compare them now; because when Courtois goes under Mourinho's/Cech's wing and experiences the EPL, there will be no comparison. De Gea is Spain's future star and will be one of the best goalkeepers of the next generation, but he is no where near as complete as Courtois is. Courtois has got exceptional height, agility, reflexes and athleticism. He also has far much less mental errors than most world-class keepers already. The guy literally has no weaknesses.
Thanks to Vendetta for suggesting this one! So will win? Two of the best young goalkeepers this year....
Both:
Courtois:
De Gea: