Hmm, interesting question. This is kind of like pondering which form of gruesome death scares me the most.
Personally I've decided that of all our array of lethal problems, the bullpen is the biggest.
Since two relief pitchers are roughly equivalent to one everyday player, I'll go with Andrew Bailey and Mark Melon Balls. I'm afraid that neither one of these guys are going to pitch a quality inning for us this year. Which would not only be terrible for our chances, but would mean we'll be subjected to an endless parade of stories pointing out how Cherington flopped with his offseason moves.