Probably the greatest are Opera stars
(I've sung both popular and classical techniques and
the classical stuff is generally much more demanding)
Luciano Pavarotti,
Placido Domingo
Joan Sutherland,
Beverly Sills
Outside of opera - the singers that impress me most with their vocal technique have been...
Celine Dion,
Mariah Carey,
Jon Anderson,
Elvis Presley,
James Taylor
DB