In the lead by a long mile: Ella Fitzgerald singing Every time we say goodbye
(1) Ella Fitzgerald Ev'ry time we say goodbye (with lyrics) - YouTube
Honourable seconds:
Emmylou Harris, Boulder to Birmingham
Tom Waits, (Looking for) the Heart of Saturday Night - the song Bruce Springsteen would have sold his soul to have written.
Dolly Parton, I Will Always Love You - ONLY in Dolly's original version; this, like Ella's Every Time demonstrates how when something's perfect you don't need to "make it better" with vocal fireworks.