Just to throw in my recommendation:

Anton Kuerti on Analekta with the Diabelli Variations.  10 CDs.

This, for me, represents the most satisfying set of the works.  It's
truly magical, and I can't think of any other recording which comes
so near to Beethoven's true spirit.  Kempff has great style, Gilels is
powerful, Ashkenazy is solid, Backhaus is individualistic, Schnabel is a
classic, but Kuerti really hits the spot everytime, IMHO!  If anyone has
had the pleasure of experiencing Kuerti's magnetism when he plays some of
these works live, let it be known that this same electricity is very well
captured on disc -I can almost imagine him performing right in front of me!
Sparkling fingerwork, uplifting bravura passages, exceptional tenderness,
great intimacy, meticulous observation of the written score, highly
spiritual - just plain FANTASTIC!

I can't recommend this set more.

Tan-Trao Phi