On a purely visual level, U.S. Agent looks top. Sporting a black, white and red rendition of the classic Cap garb, John F. Walker took over as the main Captain America from #333 onwards, filling in for Steve, who'd withdrawn from the role in light of the government's attempt to bring him in line with the Commission on Superhuman Activities.
Walker, unlike Rogers, had no such qualms. Ideologically dogmatic and the kind of patriot no one would want to celebrate, he stepped up when the government asked him to and immediately began to carve out his own persona as Cap, going so far as to abandon the identity altogether and become a new hero, called U.S. Agent.
Prior to this shift, Walker killed several villains and was placed under great psychological strain as his new responsibilities began to mount. Sensing that maybe, y'know, they'd messed up, the government convince Steve to return and take over the mantle once more, shifting Walker off into a new identity to do their dirty work as and when they need.
Later issues would see the character set up shop at the West Coast Avengers, taking a leading role on the team during the Infinity War saga before partaking in various other Avengers-related escapades later on. He's quite the thug though, and while he's more respected today than he was when he was first introduced, there's no denying that this Cap - unlike Bucky, Sam and the rest - is a poor imitation of the original.
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