Kate, one of the most popular characters on the show, just can't make up her mind. She loves Jack. Now she loves Sawyer. Now Jack. Now Sawyer. Pick one already! Her indecision is reminiscant of Favre's will he or won't he retire sentiment that seems to envelope NFL storylines each offseason. That, and they both absolutely love attention.
Ben Linus- Scott Boras
Ben Linus is evil. Everything he does, he does for his own personal gain. He doesn't care about people, their feelings, or their lives, he only cares about himself. He embellishes, tells "half truths", and often just flat out lies in order to get what he wants. All of that (and more) is true about Scott Boras. The superagent, who represents some of Major League Baseball's most talented and well-known players, is not above making up stories to get more money for his players. Earlier this offseason, Boras said the Red Sox were the front runners to land prized first baseman Mark Teixeira after Teixeira had already decided he wanted to become a Yankee. This drove up the price for New York and caused outrage in Boston. Linus is the Scott Boras of LOST.
Locke spent the first few seasons of the show looking for his place, his calling. Always valuable, Locke only recently ascended to being a true leader, and is constantly willing to do whatever it takes for his people. Pierce toiled on terrible Celtics teams for nine years before KG and Ray Allen came along. Pierce, Boston's captain, is driven by his superstar teammates and has turned himself into one of the NBA's best players. Coming back from a knee injury during the NBA Finals isn't quite walking again after being paralyzed (a la John Locke), but his value to the team can't be questioned.
Aaron Littleton- Sidney Crosby
I know what your thinking. How can Claire's baby (born on the Island in season one) be compared to Sid the Kid? Well, much of the plot of the current season revolves around him. The entire storyline regarding Kate and (now) Sun and Jack have to do with Kate being able to keep Aaron. He's young, but incredibly important to the entire show. Crosby is also young, and just as important to the league. Since he was drafted first overall by the Penguins, Crosby has been known as the savior of the NHL. Everything (at least from a marketing standpoint) revolves around Sidney Crosby. Without him, the NHL is completely different. Without Aaron, the show changes considerably as well.
Jack Sheppard- Michael Phelps
Jack is, without a doubt, the main character of the show. He is only doctor among the survivors, and becomes their leader in season one. Everybody looks up to Jack, and more often than not, he delivers for them. Phelps' rise to fame during the Beijing Olympics put him at the top of the sports world. For quite awhile, America followed Phelps carefully, waiting with baited breath for every word (especially the media) he spoke. He led all American athletes at the Olympics with his eight gold medals, but has recently been getting criticized loudly. Both have gotten into drugs since returning (Jack from the Island, Phelps from Beijing). Jack's addiction to painkillers and booze hurt his relationships with the rest of the Oceanic Six. It's unclear, at this point, how the photos of Phelps ripping a bong at a friend's house will affect his relationships (with sponsors mainly) at this point in his career.