Like all keepers, Schmikes made mstakes, and like all proactive and daring keepers, quite a few of his mistakes looked very bad (nothing like WC winner, EC winner, CL winner, PL and La Ligue winner Fabien Barthez, though).Schmeichel's main weakness was that he just made too many mistakes. Still, I would likely put him as first. De Gea a close second, VDS a distant third.
One particular thing I noticed as he played for Denmark in 90, 91 already, and that almost always bore out: He made a lot of seeming errors rushing out to catch ambitious crosses in the box and losing them, giving him a rep as sometimes error prone. What I noticed, though, was that his frenecy in retrieving the lost ball ensured that only a tiny amount of these errors led to goals against. While his active court protection made it hard to produce a lot of clear headers etc against Brøndby, Denmark and later United. Once discovering this feat of his play, it was a great joy to watch him flailing about, while mates and pundits crticized, world class strikers like Davor Suker, Jean-Pierre Papin, Dennis Bergkamp, Marco van Basten and Jürgen Klinsmann stood paralyzed and the weakest Danish team in two decades won the European Championship.
It turned out it wasn’t a fluke, most of his mistakes in the box paid off in the end.