John McCain/Jimmy McNulty
Both cultivated reputations as mavericks in their respective fields: McCain challenged Republican orthodoxy by standing up for campaign finance reform and against Big Tobacco; McNulty pissed Rawls and Burrell off by drawing attention to the bodies Avon's crew was racking up. Neither is really all that likeable, but for much of their careers one could forgive their failings because of their dedication to their work. Recently, however (the summer months of the McCain campaign/all of Season 4 when McNulty sobered up and disappeared from the show) both looked like they'd squandered their leading man status as others rose up around them. But as things started to come to a head, both got their shit together (McCain pulled out New Hampshire/McNulty went back to the sauce and, equally important, back to homicide). If you asked me a few years ago, I'd have told you these guys are the stars, but have they pissed off too many people (the Evangelical base/the entire Baltimore police department) to be left standing when the season comes to an end?