I like OPS allowed as a stat to compare pitchers. It is the stat that they have the most control over. I took the candidates, compared them to the average pitcher that played in their league in their year for every year that they pitched, and came up with an "OPS Allowed Under Avereage Pitcher OPS Allowed". Here are the results.
SP's in the HOF
OPS Allowed Under Average - .154
OPS Allowed Under Average - .091
OPS Allowed Under Average - .090
OPS Allowed Under Average - .082
I'm not sure that any belong, but if I had to vote for one, it would be Greenberg. He is by far the most decorated of the three. Additionally, there are so many pitchers better than tehse guys taht are just a couple of seasons from being eligible. I say keep the standards high.