Surprisingly hard one that, and going to have to do the wall of video as a result.
While I have no objection to vocals of either gender I had a scan through most of my music collection and at best most people doing the odd bit of backing, or maybe alternate a few verses that are essentially unrelated to each other. Something where the singers play off each other in some notable fashion... minimal really.
John Fogerty & ZZ Top brings a smile to my face but not really duet, same for
Johnny Cash and Arlo Guthrie.
I suppose we can do Fairytale of New York
However to call it my favourite anything would be a bit strong -- it is a song I don't mind at all but not much more. It is mainly here so people lose the game early.
The Hillbilly Moon Explosion - 'My Love For Evermore' is enjoyable for me
I also see the they did a cover of Jackson but I will take the original for that one
and the male vocalist (himself a noted singer in some other bands) also did another I really like
Sparky and The Deadbillys - When Death Rides A Horse
Under pressure probably counts here.
Looking through whatever I have that counts as such then I have come to the conclusion that while some duets might be individually good songs they usually have solo (or with the rest of their "normal" band) songs that are multiple times better - Mark Knopfler and Eric Clapton did a song called Someday that most bands would be delighted to have something half as good as for a lead but compared to either at their solo best (give or take some live collaborations Clapton has done)? Not a chance. Van Morrison and John Lee Hooker did a bunch together and while I am not the biggest Van Morrison fan they are both legends for a reason but checked out a bunch of their collaborations/duets and can't do it. This was also a problem I faced with another I really like a band called Eluveitie and while I like their instrumentals and when they have just their female artists or just their male artists singing their "duets" don't do as much for me.
Try Luxtos if you want though but know there is better in their catalogue
Do we count "Hit the road Jack"?
Closest I have after this is actually dangerously close to a ballad (and there goes whatever street cred I have left), and again each of those individually has some amazing stuff but this... middling at best
In case I was forgetting things I also went through a bunch of list articles. Several had artists I really liked but none had songs I particularly care to note here. I would include Je t'aime... moi non plus if only because of the outrage it caused, not to mention I like the
Judge Dread version more, even if that is by far one of his weaker "big" songs.