This is a sorted list of the best bullpens in baseball according to THE BAT's context-neutral projected 'true talent' ERA.  This incorporates, among other things, regression, multiple weighted years of data, aging, velocity, minor league and foreign league data, and adjustments to account for the quality of opposing hitters, ballparks, umpires, weather, pitch-framing, defense, and more for each reliever on the team, weighted by projected innings pitched over the remainder of the season.  Note that this includes not just the current members of the bullpen, but all pitchers expected to pitch in relief over the course of an entire season.