The pre 64's are considered to be a superior action because they were very well built. At around 1964 Winchester was revamped so to speak and they began focusing more on quanity rather than quality. This is not to say that post 64 rifles are bad because they aren't. Mine functions just fine. But the pre 64's are better.

They were machined from solid billets of steel rather than cast like the post 64's are.

They have controled round feeding rather than the push round feeding. Some consider this a plus.

The extractor is obviously much stronger than the small extractor on the post 64 rifles.

Parts were more precisely fitted to each other.

Quality control was much much better on pre 64 rifles.

The stocks were of much higher quality woods.

The bottom metal was machined from steel rather than aluminum alloy on the post 64's