I think actually is the third best in the series.
The second Apollo fight is the closest, most difficult victory of them all. That ending just doesn't get more dramatic.
The Lang rematch was fucking fire. So much at stake. After that ruthless beatdown and depression, comes a totally different Rocky, trained by Apollo, using his speed but soon breaking apart and having to change strategy, paying homage to the great Ali vs. Foreman rope-a-dope strategy to wear Lang.
The Drago fight was one sided, with Rocky reverting to his original style of using his head as a punching bag. And he turns it around in the very last round. It was highly reminiscent of Apollo 2. It was an awesome fight, but just not as creative as the others.