This is definitely "generational". My list of distinctive, instantly recognizable voices would be (not necessarily in order of talent or ability):
Elvis
Sinatra
Billie Holiday
Muddy Waters
and, to a lesser extent, because his voice has changed so much over the years,
Bob Dylan
Elvis
Sinatra
Billie Holiday
Muddy Waters
and, to a lesser extent, because his voice has changed so much over the years,
Bob Dylan