Scheimchel was by far and a way the best Utd keeper I have seen, TBH the best keeper I have seen bar none, De Gea has had 100 more games to reach the same number of clean sheets, he still falls behind VDS for me also.... maybe it is rose tinted glasses but Schmeichel used to own his area, defenders and attacker be warned he was terrifying, and people forget those long throws, god knows how many counter attacks he started with his throwing.
DeGea has shown especially this last few weeks that when at his best he is a heck of a shot stopper, I would not say as good as Schmeichel or VDS but very close, but his distribution and more importantly for me the lack of control and authority he has in the box are his biggest weaknesses, everytime we have a cross or corner I get palpitations, and yes he may make a brilliant save from a close header but in his place Schmeichel or VDS would have already claimed the ball, and Schmeichel would have probably wanged it 60 yards upfield to Rashford.
Edit: Just watched some Schmeichel highlights for a bit of nostalgia, there a lot of saves that DeGea would not have even tried to make, or even could have, Schmeichel used to stand further forward and made a lot of reactions saves on the edge of 6 yard area, narrowing the angle the striker had available and using his incredible reflexes, because DeGea never leaves his line these shots would be past him or unsaveable from his position