To speak of "the best model" is somewhat odd. Logicians have long known that there are different kinds of conditionals. As to whether the truth functional conditional that we now call the material conditional was known to medieval logicians, there is some scholarly debate on the subject.
William of Ockham, Pseudo-Scotus, John Buridan and Walter Burleigh do not appear to have explicitly described what we now call the material conditional, but all gave examples of conditionals and their role within valid arguments that seem to commit them to accepting it as a kind of conditional. Also, some of these logicians can be understood as distinguishing between material conditionals and strict conditionals and accepting both.
Philotheus Boehner, "Does Ockham Know of Material Implication?" Franciscan Studies, 1951, Vol 3/4, pp. 203-230.
Marilyn McCord Adams, "Did Ockham Know of Material and Strict Implication? A Reconsideration" Franciscan Studies, 1973, Vol 33, pp. 5-37.
E. A. Moody, Truth and Consequence in Mediaeval Logic, 1953, pp. 64-80.
David Sanford, If P then Q, 2nd edition, 2003, chapter 2, pp. 30-45.