Courtois has shown for Atletico that he can both keep his team in matches by making save after save to them win them games they do not deserve too (the Copa final vs Madrid in 2013 is a great example of that). But what he did for Atletico last season required something different and even more difficult. Atletico won some games by a big margin, but a lot of them were by a single goal or two. Because of their defensive excellence last season which was based on hard work, constant closing down and pressing, dogged displays and resilient attitude, they still conceded some chances especially late on in games when they were leading by a single goal and Courtois showed excellent concentration and alertness to make big saves at such vital moments after not being tested or given much to do all game. I am yet to see that type of concentration and ability to make saves at vital moments after having little to do all game from DDG on a consistent basis like I have seen from Courtois.
Fair enough Raul. Though, there is quite a lot of data to support the claim that De Gea has evidenced the ability to maintain his concentration and make decisive saves in matches where United were leading by a fine margin. So it's a bit disingenuous to state that David hasn't shown that on a consistent basis whereas Caourtois has.
Some opposition fans might not agree, but for the purpose of fairness, the performances of every single United player should be voided for the 2013/ 2014 season. The team had little cohesion at times, there was a lot of hidden reported resentment among the group and frankly most of them looked like they weren't arsed so broader picture, it's hard to deduce any key to individual player performances from a collective or titular perspective. If we compare De Gea's form in United's league winning 2012/ 2013 season, it makes for some interesting reading.
2012/ 2013 :
League games won by United by a single goal margin : 11.
2012/ 2013 :
League games won by Atletico by a single goal margin : 8.
2013/ 2014 :
League games won by Atletico by a single goal margin : 12.
2014/ 2015 :
League games won by United by a single goal margin : 5.
2014/ 2015 :
League games won by Chelsea by a single goal margin : 4.
So I really don't get the notion that De Gea is a fine shot stopper but doesn't have the concentration or calm mental ability of Courtois. I do honestly believe that his new-found stature in the game of being the best keeper in the world bar Neuer is largely predicated on the hyper surrounding Atletico's league winning, European Cup final competing 2013/ 2014 season.
Swap the two and I'm pretty sure De Gea would have done equally well behind the stronghold of Tiago and Gabi and Felipe and Juanfran and Godin and Miranda and Juanfran. Maybe that's the United fan in me siding with our player, but I genuinely feel I'm being impartial here. I'd readily swap Hazard some all of our wingers, or Matic and Cesc for any CM bar Herrera or Costa for RVP, so I'm not exactly conceited wrt the superiority of some of Chelsea's players when compared to their United counterparts. But I really wouldn't swap the two keepers.
EDIT : Updated !