Sean Bean played both Boromir in the Lord of the Rings movies and Stark in HBO's adaptation of Martin's novels.
"I think Boromir is probably more of a warrior than Ned was," the writer told MTV Geek. "Ned was more of a lord, a ruler, a diplomat, a general."
He added: "In simple physical one-on-one combat, Boromir probably [would win]."
In the interview, Martin also considered who would come out on top in a bout between Frodo Baggins (Elijah Wood) and Tyrion Lannister (Peter Dinklage) and between Aragorn (Viggo Mortensen) and Jaime Lannister (Nikolaj Coster-Waldau).
Sean Bean has previously stated that he is keen to return to Game of Thrones as the late Ned Stark, revealing that a flashback sequence featuring his character is "a possibility" in future.
Game of Thrones returns to HBO for a third season on March 31, 2013 and airs on Sky Atlantic in the UK.
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Watch George RR Martin talk Game of Thrones and Lord of the Rings below: