“A jury consists of twelve persons chosen to decide who has the better lawyer” is a popular joke definition of a jury. The joke appeared in the Atchison (KS)

in January 1904:
   
“A Hindoo who visited this country to study its institutions, visited the court house. ‘What’s the jury for?’ he inquired. ‘To decide which side has the better lawyer,’ his guide replied.”
   
“JURY—Twelve men chosen to decide who has the better lawyer” was published in The Foolish Dictionary (1904) by “Gideon Wurdz” (Charles Wayland Towne). “Men” would be replaced with “persons” when women were finally allowed to serve on juries.
 
The saying is often credited to American poet Robert Frost (1874-1963), but Frost—if he ever said it—did not originate or popularize the line. Frost was unknown in 1904, when the jocular definition made many newspapers. French novelist and playwright Honoré de Balzac (1799-1850) is also sometimes credited, but there is no evidence that Balzac said it, either.
 
 
Chronicling America
27 January 1904, Topeka (KS) State Journal, “Globe Sights” from the Atchison Globe, pg. 4, col. 2:
A Hindoo who visited this country to study its institutions, visited the court house. “What’s the jury for?” he inquired. “To decide which side has the better lawyer,” his guide replied.
     
Google Books
The Foolish Dictionary:
An Exhausting Work of Reference to Uncertain English Words, Their Origin, Meaning, Legitimate and Illegitimate Use
By Gideon Wurdz (pseudonym of Charles Wayland Towne—ed.)
Boston, MA: John W. Luce and Company
1904
Pg. ?:
JURY Twelve men chosen to decide who has the better lawyer.
 
31 May 1904, Denver (CO) Post, “The ‘Foolish Dictionary,’” pg. 4, col. 3:
JURY—Twelve men chosen to decide who has the better lawyer.
 
4 January 1951, Cullman (AL) Banner, “Bama Bob,” pg. 6, col. 2:
Jury—Twelve men who decide who has the better lawyer.
 
Google Books
Courts on Trial:
Myth and Reality in American Justice
By Jerome Frank
New York, NY: Atheneum
1971 [©1949]
Pg. 122:
The foregoing tends to justify Balzac’s definition of a jury as “twelve men chosen to decide who has the better lawyer.”
 
Google Books
And I Quote:
The Definitive Collection of Quotes, Sayings, and Jokes for the Contemporary Speechmaker (Revised Edition)
By Ashton Applewhite, William R. Evans III and Andrew Frothingham
New York, NY; Thomas Dunne
2003
Pg. 439:
A jury consists of twelve persons chosen to decide who has the better lawyer.
—Robert Frost (attrib.)
     
Google Books
The Yale Book of Quotations
Edited by Fred R. Shapiro
New Haven, CT: Yale University Press
2006
Pp. 294-295:
Robert Frost
U.S. poet, 1874-1963
A jury consists of twelve persons chosen to decide who has the better lawyer.
Attributed in Evan Esar, The Dictionary of Humorous Quotations (1949). Although this is usually attributed to Frost, it appears without attribution to any individual in John Garland Pollard, A Connotary (1933). In Pollard’s book the wording is “JURY—Twelve men chosen to decide who is the best lawyer.”
 
Google Books
The Biteback Dictionary of Humorous Business Quotations
By Fred Metcalf
London: Biteback Publishing Ltd.
2014
Pg. ?:
A jury is twelve people whose job it is to decide which side has the better lawyer.
Robert Frost,