I would go with The Quiet Man, closely followed by The Man Who Shot Liberty Valance. Some of Ford's movies are below to refresh your memory.
Stagecoach (1939)
Young Mr. Lincoln (1939)
Drums Along the Mohawk (1939)
The Grapes of Wrath (1940)
How Green Was My Valley (1941)
My Darling Clementine (1946)
She Wore a Yellow Ribbon (1949)
3 Godfathers (1948)
Rio Grande (1950)
The Quiet Man (1952)
The Long Gray Line (1954)
The Searchers (1956)
The Horse Soldiers (1959)
The Man Who Shot Liberty Valance (1962)
Stagecoach (1939)
Young Mr. Lincoln (1939)
Drums Along the Mohawk (1939)
The Grapes of Wrath (1940)
How Green Was My Valley (1941)
My Darling Clementine (1946)
She Wore a Yellow Ribbon (1949)
3 Godfathers (1948)
Rio Grande (1950)
The Quiet Man (1952)
The Long Gray Line (1954)
The Searchers (1956)
The Horse Soldiers (1959)
The Man Who Shot Liberty Valance (1962)