I can see why you ask as a list like this could be virtually endless. Add to to that all the different performances of the same pieces at different times and you realise this could make assembling a system seem like a doddle! It might be a good idea first to determine which instruments and sub genres of Classical you like best eg vocal, piano, harpsichord, guitar, quartets, symphonies etc.
However, having said all that, for my money two piano pieces stand out above the rest.
Rachmaninoff Piano Concerto 2.
All versions all good, how could they not be?
My favourites are the ones by Kissin and Ashkenazi.
https://youtu.be/l4zkc7KEvYM
Glenn Gould’s Goldberg Variations are also indispensable for me.
Both the 1955 first attempt and the 1981 slowed down version.
Even the reimagined Zenph 1955 recording is full of brilliance.
https://youtu.be/Ah392lnFHxM
However, having said all that, for my money two piano pieces stand out above the rest.
Rachmaninoff Piano Concerto 2.
All versions all good, how could they not be?
My favourites are the ones by Kissin and Ashkenazi.
https://youtu.be/l4zkc7KEvYM
Glenn Gould’s Goldberg Variations are also indispensable for me.
Both the 1955 first attempt and the 1981 slowed down version.
Even the reimagined Zenph 1955 recording is full of brilliance.
https://youtu.be/Ah392lnFHxM