A very tricky question! Speaking for myself, it really depends when a person asks me! But for the moment, it's "The Pay Off" by the California Ramblers. Although it'll probably be replaced next week by something else
Today it's Nellie Lutcher "The One I Love Belongs to Somebody Else."
Tomorrow, who knows? Maybe "Where Did Robinson Crusoe Go With Friday on Saturday Night?" by Jolson.
My 'song du jour' is John Henry or Go Down, Moses by Paul Robeson. Both on blue label Columbia from 1940-something. I really like most things Robeson recorded.
I am rather fond of Collins and Harlan's last Diamond disc, "Any Way the Wind Blows". I bought it at the Valente's (APSCO) old retail store in New York back in the 70s even before I owned a Diamond Disc player!