Since it’s a subjective question all I can offer is my opinion. For male vocalists it is Peter Green from Fleetwood Mac, not because he had all of the range of a Freddie Mercury, but because of the emotive style in which he sang. He was perfect for the blues rock genre & doesn’t get the recognition for his vocal talents as he does for his guitar work. Honorable mention goes to Dave Edmunds as well as Al Stewart, George Benson, Phil Lynott, Steve Winwood, & Ian Gillan. I’ve always had great respect for the vocal talents of Jim Croce, Gordon Lightfoot, & Jack Bruce as well.

For female vocalists it would be jazz singer Nancy Wilson. She had a beautiful voice, excellent range, & was a great interpreter of any composers’ work. For me there was none better. Other than jazz listeners not many know much about her though. Honorable mention goes to Imelda May who I personally feel is the best female vocalist active today, Julie London, Flora Purim, Astrud Gilberto, Chrissie Hynde, & Allison Krauss.