Who is the best singer of the world ?

That's kind of a silly question given the wide variety of musical styles there are.  That's why you've gotten so many silly answers.

My own favourite living singer is Wesla Whitfield.  Take a listen at:

https://www.youtube.com/watch?v=Fcm7vUDfGgc

Hers is an amazing story.  Read at:

http://articles.latimes.com/1999/apr/18/news/mn-28533