Just my opinion, but the best are from the 50s-60s. The fit (internal and external) just seems more precise and the actions seem a step above the norm. That span might include the late 40s as the few I've seen have looked rather nice.

Given a decent price, I wouldn't turn any Marlin down made before 2009.

"A free people (claim) their rights as derived from the laws of nature, and not as the gift of their chief magistrate."
--Thomas Jefferson, Rights of British America, 1774