Not to jump on the bash-CSO-bandwagon, but I have to admit that though a horn player, I wasn't a fan of the Solti/CSO Strauss recording that I knew before I heard the Guilini recording of M9 (in '78 or '79 I think). In fact, I wasn't impressed by Mahler at the time after sampling many recordings from the university library's stacks of LPs (probably Karajan, Horenstein, Haitink). However, I received the Guilini M9 as a gift from my younger sister, and I listened to it straight through twice with head phones, and that recording was my 'Mahler epiphany'. Sure, the strings are thin at times (and wow were the cellos-with-tremolos weird in the early CD version), but it remains a favorite.
Regarding Gilbert's version, I tried all the usually-recommended single-disc versions, and his is the one that resonates with me.