I'm going to go for Raging Bull here.
As has been pointed out with Full Metal Jacket, A Clockwork Orange is a film with a great first half and a so-so second. Aside from the oft-referenced scene of Alex being forced to watch barbaric scenes so as to be "reprogrammed", a lot of the big scenes happen early on and it is an incredibly tough task to keep such strong momentum going.
Raging Bull is far more measured throughout its running time as Jake struggles with getting the right fights, getting the right girl, getting his weight sorted, keeping out of trouble with friends, family and the law. Throughout each new struggle, Robert De Niro is almost hypnotic as you see his own fears simmer below the surface and under Scorsese's direction he gives one of his strongest performances. From his bouts against Sugar Ray Robinson and ascension to the title, to the depths of despair he sinks to when he is incarcerated for allowing teenage girls into his club and relentlessly pounds the wall in anger and frustration, Raging Bull is a hell of an emotional journey and should KO Alex and his droogs.