Thats f***ing tough.
I cant decide since there are different types of blues and each has its 'best' list of its own.
John Lee Hooker will always be the guvnor, Robert Johnson, BB King, Buddy Guy, Jimi Hendrix
Elmore James and Stevie Ray Vaughn are probably the bluesiest guys I can think of that never seen to get old for me. (And that influenced me as a guitar player too)