Arguably:
Pre-1964 milled steel rifles and most sought after - aka: the best
1964-1970 hollow pins & stamped action parts that really reduced overall quality - aka: the pits
1971 some ALL of the the cheaper parts replaced with higher quality parts - action pins/lifter/etc 1971-1981 Rifles were still being produced by Olin/Winchester - The best of the post-64's. Pre-safety, pre-rebounding hammer, pre-AE
1981 Rebounding hammer introduced - an abomination IMHO
1982 rifles contracted out SOLD to (new company) US Repeating Arms for production - Same as post 1971, better (not "best") quality
19821983 Angle Eject becomes standard
1992 cross bolt safety added, 2003 2004 safety changed from crossbolt to Tang Safety - Same difference, both safeties unliked, some users prefer one to the other
2006 the funeral
2009 Who knows ?