An argument could be made that Marmol is the most valuable to the team for the time he's out there, but as a reliever his overall contribution simply can't compare to a starting pitcher or a positional player. http://www.hardballtimes.com has a Win Share "rate" stat that measures value per time, and Marmol does lead the team in that category (among players that actually logged significant time) Also, I suppose if you wanted to look at it empirically (and really like Win Shares), 3 win shares = 1 win, so I suppose the Cubs wouldn't be in first place without any one of the players with at least 6 win shares. That includes Ramirez, Lee, Soriano, DeRosa, Zambrano, Theriot, Jones, Hill, Lilly, Marquis, Floyd, Marmol, Dempster, and Howry. Sounds about right.