My problem with threads like these, is I could never pick out 20 albums as my favorite, that I could consider better than all the rest.
I listen to the following genres and some of their subgenres:
Prog (avant-prog, Canterbury, Zeuhl, symphonic-prog, prog-metal)
Classical (avant-garde, serial, atonal, New-Complexity, Spectralism, 12 tone)
Jazz (fusion, post-bop, avant-garde, M-Base, chamber-jazz)
I could easily pick out 20 from each genre, that I would consider as good as the top 20 from the other genres. And I could also pick out quite a few more for each of each genre that are the equal of some that are on each list.
So, I am going to cheat and create 3 lists, 1 for each genre.
Artist - Album - Song
Prog:
Yes - Close to the Edge - Close to the Edge
Genesis - Selling England By the Pound - Dancing Out With the Moonlit Knight
King Crimson - Larks' Tongues in Aspic - Larks' Tongues in Aspic, Part 1
PFM - Storia di un Minuto - Appena un po
Magma - KA - Köhntarkösz Anteria
Area - Arbeit Macht Frei - Arbeit Macht Frei
Anglagard - Hybris - Vandringar I Vilsenhet (Wanderings in Confusion)
National Health - Of Queues and Cures - Dreams Wide Awake
Gentle Giant - In a Glass House - In a Glass House
Echolyn - Suffocating the Bloom - A Suite for the Everyman
Univers Zero - Heresie - Vous le Saurez en Temps Voulu
ELP - Tarkus - Tarkus
Pain of Salvation - Remedy Lane - Beyond the Pale
Van Der Graaf Generator - Pawn Hearts - A Plague of Lighthouse Keepers
Eskaton - 4 Visions - Eskaton
Banco - Io Sono Nato Libero - Canto Nomade Per Un Prigioniero Politico
Thinking Plague - In Extremis - Les Etudes d'Organism
Frank Zappa - One Size Fits All - Inca Roads
Jethro Tull - Thick as a Brick - Thick as a Brick
Museo Rosenbach - Zarathustra - Della Natura
Mike Oldfied - Ommadawn - Ommadawn Pt 1
Jazz:
Return to Forever - Romantic Warrior - Duel of the Jester and the Tyrant
The Art Ensemble of Chicago - Urban Bushman - Uncle
Mahavishnu Orchestra - Apocalypse - Vision is a Naked Sword
John Coltrane - A Love Supreme - Pursuance
Alice Coltrane - Ptah, The El Daoud - Mantra
Brand X - Unorthodox Behavior - Nuclear Burn
Weather Report - Black Market - Elegant People
Anthony Braxton - Six Compositions: Quartet - Unpk X [Composition No. 40B]
McCoy Tyner - Sahara - Sahara
Iceberg - Sentiments - Alegries Del Mediterrani
Keith Jarrett - Koln - Part I
John Abercrombie - Timeless - Lungs
Terje Rypdal - Whenever I seem to be Far Away - Silver Bird is Heading For the Sun
Allan Holdsworth - Metal Fatigue - The Un-Merry-Go-Round
Bruford - One of a Kind - Fainting in Coils
Miles - In a Silent Way - Shh/Peaceful
Steve Coleman and the Council of Balance - Synovial Joints - Harmattan
Jean Luc Ponty - Enigmatic Ocean - Enigmatic Ocean
Alex Machacek - 24 Tales - Sweet Torture
Oregon - Out of the Woods - Waterwheel
Mary Halvorson - Amarylis - Night Shift
Classical:
Elliott Carter - Concerto for Orchestra (1969)
Beat Furrer - Konzert, for piano and orchestra (2007)
Anna Þorvaldsdóttir - CATAMORPHOSIS (2020)
Bruno Maderna - Concerto for oboe and orchestra No.3 (1973)
Charles Wuorinen - Fourth Piano Concerto (2003)
Magnus Lindberg - Sculpture (2005)
Joan Tower - Concert for orchestra (1991)
Milton Babbitt - Concerto for Piano and Orchestra (1985)
Kaija Saariaho - Laterna Magica (2009)
Bela Bartok - Music for strings, percussion, and celesta (1936)
Igor Stravinsky - The Rite of Spring (1913)
Alban Berg - Violin Concerto (1935)
Unsuk Chin - Violin Concerto (2001)
James Dillon - Helle Nacht (1986-87)
Samuel Barber - Piano Concerto (1960)
Tōru Takemitsu - From Me, Flows What you Call Time (1990)
Olga Neuwirth - Remnants of Songs ... An Amphigony for viola and orchestra (2020)
Arnold Schoenberg - Variations for Orchestra (1926)
Augusta Read Thomas - EOS (Goddess of the Dawn), for orchestra (2015)
Krzysztof Penderecki - Violin Concerto No. 2: Metamorphosen (1992–95)