It's hard to say something about Brendel's claim unless knowing a bit more about WHY he thinks it is the best piano piece ever written.
I have heard the same thing about Brendel. I have always enoyed this piece--hauntingly beautiful. I choose where I play it, if they are not comfortable with classical music, might not be a good choice--since it is rather long---and if you do the repeats. But when played well--people love it. I adore the Rondo in a minor even more. If you are learning this for the first time----record yourself---alot. You want to make sure your rhythm has pulse---direction---and your line sings and is phrased very well. Too slow a tempo---and you lose the line.Kitty on the keys