Mahler on vinyl - your favorite

Mahler 1st with Solti and the London Symphony (better than the later Chicago disc.)

Mahler 9th Barbirolli, on Classics for Pleasure label.  Outstanding performance and sound.

Your moniker suggests sound quality is of importance, so with that taken in consideration:

no.1: Walter on US Columbia

no.2: Klemperer on UK Columbia (emi)

no.3: Mehta on Decca/London

no.4: Szell on US Columbia or UK Columbia (emi)

no.5: Barbirolli on HMV (emi)

no.6: Barbirolli on HMV (emi)

no.7: Solti on Decca/London

no.8: Solti on Decca/London

no.9: Walter on US Columbia

Lied von der Erde: Klemperer on UK Columbia 

I realise that the original issues of some of these recordings are in the collectors category and priced accordingly. In those cases (like the Klemperer no.2) you should try to find an early reissue, which usually will sound pretty good for much less. Enjoy the ride!

+1 @crustycoot  Great example is the Abbado/Chicago Resurrection.  The original lps were trashed by critics because the important offstage band was inaudible.  It was in the grooves but cartridges of the day couldn’t reproduce it.  The CD places it in perfect perspective relative to the main Orchestra 

The Abbado Chicago Resurrection was cut for the LP at a very low level, too low a level, and cannot be recommended.  Perhaps better in digital.

I agree and so will not repeat any of the above recommendations.

Songs of the Wayfarer, Fischer-Dieskau, Kubelik, DG (forget the attached 5th)

Sym 1, Horenstein, London Sym, Nonesuch

Sym 5, Abbado, Chicago, DG

Sym 7, Bernstein, NY, Columbia

Sym 9, Haitink, Concertgeboew, Phillips

Sym 10 Adagio, Boulez, London Sym, Columbia

Das Lied von der Erde, Walter, NY, Columbia

All of these hold there own into the digital era.