Give your favorite in the different categories: Best ALL-TIME... 1. ...COMPOSER. 2. ...SYMPHONY. 3. ...OPERA. 4. ...MASS. 5. ...PIANO CONCERTO. 6. ...STRING QUARTET. 7. ...OVERTURE. 8. ...PIANO SONATA. 9. ...SYMPHONIC POEM. 10....VIOLIN CONCERT.
I can not nominate only one in each categorie. 1) Composer: Equality of votes for Mozart, Beethoven and J.S.Bach. 2)Symphony: Beethoven's 3rd,9th., Mozart's "Jupiter", Brahms's 4th, Schubert's 9th. 3)Opera: Don't know too much about opera. 4)Mass: Beethoven's Missa Solemnis, Mozart's Requiem, Bach's Mass in Bm 5)Piano Concerto: Beethoven's 4th and 5th. 6)String Quartet: Beethoven's opus. 131 and op. 132. 7)Overture: Mozart's La Nozze di Figaro. 8)Piano Sonata: Beethoven's 30,31 and 32nd, Liszt's sonata in b. 9)Symphonic Poem: Richard Strauss's "Don Juan" and "Alpine Symphony" 10) Beethoven's one, Tchaikovsky's one, Mendelsshon's one, Bruch's one and Brahms's one.
I feel I need to list more than one also. They are in order --- 1: Composer - Mozart / Shostakovich / Brahms; 2: Symphony - Mozart #40 G minor / Tchaikovsky #6 Pathetique / Beethoven #3; 3: Opera - Magic Flute / Marriage of Figaro; 4: Mass - Mozart Great Mass in C Minor K427 / Bach B Minor / Mozart Requiem; 5: Piano Concerto - Mozart #20 & #27; 6: String Qt - Shostakovich #8 / Barber B Minor (Second movement is the "Adagio for Strings"; 7: Overture - Magic Flute / Shostakovich Festival Overture; 8: Piano Sonata - Mozart Sonata A major K331 (with Turkish Rondo) / Schubert Sonata D960; 9: Poem - Smetana "Ma Vlast" / Debussy "La Mer"; 10: Violin Concerto - Goldmark / Tchaikovsky / Mendelshon MANY MORE HONORABLE MENTIONS.
I also can’t just have one per category so I’ve listed those that I think are works of the first rank. I also have listed what I think is a recording of the first rank for each.

1. Composer: Beethoven, Bach, Mozart, Haydn, Monteverdi, Bartok.

2. Symphony: Beethoven 3 (Toscanini 1938), Beethoven 9 (Furtwangler Lucerne), Beethoven 5 (Kleiber), Bruckner 8 (Karajan/Vienna), Haydn 88 (Bruggen), Beethoven 7 (Kleiber), Mozart 41 (Toscanini), Brahms 4 (Kleiber), Brahms 1 (Karajan).

3. Opera: Marriage of Figaro (Kleiber), The Ring (Solti).

4. Bach Mass: in Bm (Richter), Monteverdi Vespers (Munrow), Missa Solemnis (Gardiner).

5. Piano Concerto: Beethoven 4 (Fleischer), Mozart 27 (Perahia).

6. String Quartet: Beethoven Op 130, 135 (Italiano), Haydn Op 76 (Lindsay), Bartok 5 (Tokyo), Mozart “Haydn” Quartets (Italiano), Ravel (Italiano).

7. Overture: Marriage of Figaro (Kleiber), Freischutz(Kleiber).

8. Piano Sonata Beethoven 29 (Brendel), 23, 21, 14, 8 (Schnabel or Brendel), Liszt Bm (Argerich).

9. Tone Poem: Berlioz Symphonie Fantastique (Gardner), Strauss Zarathustra (Reiner 1954).

10. Violin Concerto: Brahms (Heifitz or Vengerov), Beethoven (Heifitz).

Plus Bach is way under represented because of the categories chosen. Works by him that belong in this august company are Art of the Fugue (Walcha), Tocatta and Fugue in Dm (Koopman), Violn sonatas and partitas (Milstein), Cello Sonatas (Casals), The Well Tempered Clavier (Gould)
I suppose by now it is considered an "old war horse", but Sheherazade still to this day gets my juices flowing. I still have the same Lp my parents gave me in 1970 and it remains my favorite version, both musically, and, sonically.
One of each, huh? I'll try: 1)J.S. Bach--there are many great composers, but this man's works are still the standard for me, and I'm not a big Baroque fan otherwise. 2)too many--Beethoven 7th, Scubert 9th and Brahms 1st and 4th for the 1800s, Shostakovich 1st (and he was only 19!), Copland 3rd and Mahler 9th for the 20th Century. 3)I pass, I'm not an opera buff; however, as some called it his greatest "opera", can I nominate the Verdi Requiem? 4) Bach Mass in B Minor (by far the most difficult piece I've ever had to learn to sing). 5) Rachmaninoff 3. 6) Debussy (can't remember which one, though); if I can cheat and add a clarinet, the Brahms Clainet Quintet, probably my favorite chamber piece. 7) Morning Noon and Night in Vienna, Suppe, and anything by Rossini. 8) Liszt B minor. 9) Sheherezade, if only because of the Reiner version; also Ma Vlast, Smetena. 10) Brahms, with the Barber also up there. Too many more to mention, too....