As previous posters mentioned it is really hard to single out one release but here we go .... :
I`m a dedicated follower of Sviatoslav Richter and this 11 CD Box captures the first public performances on North American soil. At that time Sviatoslav Richter was in his early prime and the two (out of seven) are either mainly (First recital :: October 19th, 1960) or completely (Sixth recital : December 23rd, 1960) dedicated to Beethoven Piano Sonatas. He performs these - without any safety net or second bottom - splendidly (listen his Sonata 23 “Appassionata” from October 19th, 1960 !!)
PS 1 Omitting his stand-out Beethoven abilities Richter deals with other composeres (Chopin, Rachmaninov, Prokofiev etc) extremely well
PS 2 Amazon.com has this already as "Temporarily out of stock"