Holliday vs. Bay: D is the difference

Given a relatively weak free-agent class and a stagnant economy, the baseball world is unlikely to see any Mark Teixeira- or CC Sabathia-sized blockbuster deals this winter. Nonetheless, the consensus regarding the current crop is that left fielders Matt Holliday and Jason Bay are the top two hitters available, and with four of the game's six highest-payroll teams -- the New York Yankees, the New York Mets, the Boston Red Sox and the Los Angeles Angels -- among those with vacancies in left or at designated hitter, it stands to reason that both will net tidy deals. What separates the two players?