What are your top three favorite classical compositions?

Three!? Seriously!

I could never narrow it down to just three, even 10 wouldn't be able to cover all the classical music I rate equally highly. So, I will have to cheat. 😉

I am only into: 20th century, atonal, serial, avant-garde classical music. Mostly from post 1950 to the present.

Alban Berg - Violin Concerto 

Elliott Carter - Concerto for Orchestra 

Charles Wuorinen  - 4th piano Concerto 

Joan Tower  - Concerto for Orchestra 

Ernst Krenek - Static and Ecstatic 

Magnus Lindberg  - Sculpture

And a few, less 'thorny' sounding pieces:

Bartok - Music for strings, percussion, celesta

Samuel Barber - Piano Concerto 

Stravinsky - The Rite of Spring 

Again, there are many other pieces that I rate as highly as those I listed. If I made this list tomorrow, it could be almost completely different. 

Bach Goldberg variations, Elgar enigma variations, Beethoven’s seventh Symphony

Out of thousands, you jest! But I do seem to listen more often to solo piano music by Chopin, Debussy, Beethoven, Brahms, Schubert, Schumann, and Prokofiev than most others. 

How about you?

You’re right!  
Three is a near impossible task. And, as was said, it might be different tomorrow. 
 But, here goes:

 Mahler 9th Symphony 

Mozart Requiem

Almost any Mozart Piano Concerto (cheating)

I'm not "seasoned" enough as a Classical listener (only 20 years or so) to have definitive faves yet..

I Do however agree with my go to FM stations 2022 #1 pick

Ludwig V's 9th.

The Classical California Ultimate Playlist Returns | See What Made The List - Classical KUSC

Perhaps a generic/vanilla pick for discerning Classical afficionados, but the history/story behind the piece and Ludwig V's debut performance left me intrigued and a fan since learning about it.

The 2nd movement played VERY loud of my pristine 1959 RCA Living Stereo press never fails to catch my attention.

Of the countless interpretations of this masterpiece, this one is my favorite. Strongly recommended for anyone building a Classical collection with "Golden Age" Living Stereo LP's.

Cheap, probably "better" than most reissue or audiophool  copies.