For instance, David, who is our best sayer (?), said, "...".
For instance, David, who is our star, said, "...".
You do not need to use a noun that indicates that "David" speaks - the verb "to say" does that job.
Star has been used in this sense in English for over 1000 years:
OED
Star (n.) 4. figurative and in figurative contexts.
a. A person or thing likened to a star, esp. one considered as a source of inspiration or enlightenment.
lOE St. Giles (Corpus Cambr. 303) (1980) 106 Ðus wynsumlice gaderode se ælmihtiga God þas twegen scinende steorran [sc. the two saints] on annesse þæt hi þurhscinen eal þone eard þe hi onwunodon mid heora byrhta leoman.
1833 C. Lamb Barrenness Imaginative Faculty in Last Ess. Elia 182 Quixote—the errant Star of Knighthood, made more tender by eclipse.
This use has more or less combined with
c. Originally Theatre. A very famous or popular actor, singer, or other entertainer; spec. one who has top billing or takes the leading role in a film, play, etc.
1808 Monthly Mirror May 405 The star, however, of this company is Mr. Bradbury.
And the use has broadened to encompass sport
2012 N. L. Macht Connie Mack viii. 149 He felt that he would never be a star and baseball had no future for him.
and general life
e. A person who ‘shines’ or has a brilliant reputation, esp. one who is illustrious, influential, or accomplished in a particular sphere; the most notable or outstanding person on a specified (social) occasion.
1987 R. Hall Kisses of Enemy (1990) i. xvii. 104 Sir William, bent on being the star of the occasion, took an instant loathing to the portrait in which he could see a successor to some of his own dear privileges.
2015 Daily Nation (Kenya) (Nexis) & Mar. Cheating in national examinations has taken the shine off former academic stars.