Natural sounding vocals with little to no artifacts attached for me is of paramount importance on a recording.
"The illustion of, in the room with you kind"
To add from my suggestions above , another one that stands out that is readily available and inexpensive is Joan Baez "Diamonds and Rust"
I never did care for Joan's music until I heard this A&M release through a pair of Quad 63's some 25 plus years ago.
The original release was exceptionally well recorded and the current re-issue is it's equal.
Great band and good music.
Alison Krauss "So Long so Wrong" Good music, talented band, good recording however the studio mucked with the vocals too much.
Their "Live" release has far more natural sounding vocals and is equally entertaining and well recorded. Mobil Fidelity
Joe Williams "Me and The Blues" Speakers Corner , check this one out.
Nat Cole "After Midnight" mono , Pure Pleasure...in deed it is.