The problem with following this thread is the original question.   This states that Ellington has already been defined, by someone, as the voices of jazz!

If you accept this choice, or not, it seems to me that the basis of the choice was that Ellington was a) a well known name assosciated with jazz and b) someone who played traditional stuff and self pened stuff.

On that basis my choices would be:
USA - Pete Seegar
Eng - Ewan McColl
Ire - Christy Moore
Sct - Archie Fisher
Wales - hasn't got one

Paulo