Well I´m not an expert but the best singer I ever heard is F. Mercury (R.I.P.) Now I know that he wasen´t as good live as he was on albums but his voice combined with his stage preformence live made him the king not to mention his voice on all Queen albums.

He mastered evrything, high, low, gospell, rock, pop, 50´s rock n´ roll, blues...simply the best!!!