For me that would be the Dvorak Symphonies, conducted by Rafael Kubelik. 
You mean the 7-8-9 2CD set? Because I cannot
stand his performances of 1-2-3-4.
Steve - you almost stole my choice. However, my choice is this CD:

Which contains not only the Brahms 4, but also the Schubert Unfinished and two tracks from
Tristan und Isolde. I own both of these discs

, and when I saw this thread title I knew the Brahms-Schubert-Wagner CD was my choice (it's subtitled "Tribute to a Unique Artist", if I remember correctly). It's a CD that everyone -
everyone - should own. I've given it to friends who don't listen to classical.