Who’s The Best GM In Baseball?

The job of a Major League general manager is an extremely demanding one.  Player acquisitions are complicated, from trading with other teams to negotiating with agents.  Beyond working with the rest of the baseball operations staff on transactions and contract issues, the GM must communicate with scouts, coaches, medical staff, and the media, and prepare for the draft.  Our question today: who's the best?  Please note that while some of these people do not technically have the title of GM, they seem to be the team's closest approximation.