I believe a rather rarely mentioned Mahler 1 contender is Herbert Kegel whose performance with Dresdner Philharmonie from 1979 (released in 1981 on Eterna) mirrors in a passionate and colourful treatment .... and speaking about "left fielders", what about the "live" recording by Kyril Kondrashin and NDRSO @ Concertgebouw on March 7th, 1981 .... quite some choices ....