Best lefty off all time? My vote is Koufax!

[G1911]

Johnson would be my #2 pick. That his first season where he was notably above the league average was at age 29 is largely offset by his great effectiveness over age 40.

There are the 7 best (leaving Kershaw out; it is exceptionally difficult and unbalanced to account a player who is not done. His ERA+ will decline significantly, balanced by his effective innings increasing but who knows exactly how this will balance or when he will stop) + the 2 super short careers

ERA+
Grove - 148
Johnson - 135
Ford - 133
Koufax - 131
Newhouser - 130
Hubbell - 130
Plank - 122
Spahn - 119
Carlton - 115

Innings
Spahn - 5,243
Carlton - 5,217
Plank - 4,495
Johnson - 4,135
Grove - 3,940
Hubbell - 3,590
Ford - 3,170
Newhouser - 2,993
Koufax - 2,324

Black Ink
Grove - 111
Spahn - 101
Johnson - 99
Koufax - 78
Carlton - 69
Hubbell - 51
Newhouser - 47
Ford - 41
Plank - 15

Gray Ink
Spahn - 374
Grove - 319
Plank - 291
Carlton - 285
Johnson - 280
Hubbell - 252
Ford - 234
Newhouser - 180
Koufax - 151


If we have to pick one thing, the most important attribute of a pitcher is to give up as few runs as possible. His effectiveness at doing this is, in the context of an all-time debate, has to be measured relative to the context in which events actually happened, in time and place; which means ERA+. Innings Pitched is the balance to this; a pitcher who hurls a 0.90 ERA for 1 year is clearly not the best ever; how long a pitcher is effective is the other half of the equation.

Black and Gray ink I think are the best of the modern analytics, again in the context of "best all time". Black Ink is preferable, but a player CAN benefit or be hurt by not having their peak align with some other legends (Johnson suffers in black ink due to Maddux). It also matter where the ink comes from; I wouldn't value the categories in the same 1/2/3/4 point order assigned by the formula. Spahn gains a lot of his from wins, which I don't think are actually an effective metric to determine a pitchers performance.

These aren't everything, but I think these should be the starting points. Grove's ERA and league domination + a good, but not great, inning count puts #1 pretty easily in my book. Johnson seems to me pretty clearly the #2 as well. Spahn wins #3 without much difficulty, I think. After that, it gets harder to pick.

How one weighs different values, any of these 3 can reasonably be assigned the title of the greatest lefty of all time. Johnson and Spahn have excellent cases. The statistical and logically consistent reasons to pick between these three, and not anecdotal, emotional, and logically contradictory arguments based on what seems to currently favor the pitcher we want to win, are what the real debate should be.

If I have a bias for any of these pitchers, it is in favor of Randy Johnson.