Forgive the hyperbole, but there's an argument that no reliever's had a more dominant season than ZB had this year. (I saw some sabermatrician argue the other day that Miller's season was just as good, but that ERA of, what, 0.56, stands out like a "huh"?)
Miller's fielding-independent pitching (FIP)---what he threw and its results
without his defense's help---was 1.53, and his walks/hits
per inning pitched rate (WHIP) was 0.55. Britton's FIP was 1.94 and his WHIP was 0.84. That tells you that Britton got a bit more help from
his defense than Miller did, though not by much. There's almost not a dime's worth of difference between them, but my nickel goes to
Miller.
In case you'd like to compare them in postseason pitching, Britton worked in six games in the 2014 postseason, with a 3.86 ERA and a
2.14 WHIP over the six, though he did get credit for four saves. Miller, in fact, was his teammate in 2014 and outpitched him by a
considerable margin. Overall, Miller has pitched in twelve postseason games including this season's Indians games; his complete jacket:
no earned runs surrendered, no earned runs, three walks to 31 punchouts, and a 0.45 WHIP. Even allowing that he's gotten to work
more postseason innings, I'll take Miller over Britton by a hair.
But I still think Showalter made a colossal blunder not bringing in Britton to face Encarnacion . . .