I was assuming that a team would challenge the Yankees. Maybe not.
Unfortunately, I think the answer is the New York Yankee organization. In 107 years, the Yankee organization has a total of 26 World Series crowns (roughly 24.3 %). I would think the Marlins are right up there as well...they've won 2 championships in 15 years (13.33 %).
I'd be curious to know how many baseball fans realize that the Yankees started out as the Baltimore Orioles?