is the best male singer but he definitely has a beautiful voice...

but

Donny Hathaway (who Stevie Wonder was influenced by) gets my vote. He had the technical mastery due to classical training but he also was arguably the most soulful singer of his era and beyond because of the church influence.

There's so many great singers though and it really comes down to a matter of personal taste and choice.

You have singers like Lutha who had one of the smoothest and most unique tenor voices ever.

There's El Debarge who had a great voice.
MJ of course.
Maurice White, another great singer.

There's so many that its hard to pick one.