There are four significant names that have been drilled into everyone’s
head’s during the 1990’s and early part of this decade.  Four sure-fire
Hall of Famers.  Four of the greatest pitchers to ever step on a mound,
any mound, in any country, and in any world–any galaxy for that
matter.  I could see any of the four being placed into the top ten
pitchers of all time, and they all played during roughly the same
time-frame. 

These four clearly separated themselves from the rest of the crop of
pitchers during their careers.  There was them…and everybody else. 

This list will contain the top five pitchers however, because “top five” lists
sound much cooler than “top four.”  Who cares about the four best? 
People want 5!  🙂

But anyway, open for debate as always, here are the five best pitchers of the past 20 years…

Included is career ERA+ (ERA Adjusted for ballpark and league)

• Pedro Martinez:  ERA+ 154:  Mariano Rivera recently, within the
  past year, moved to the top of the ERA+ leaderboard on
  BaseballReference.com.  And I have to admit that I am not happy about
  it.  But Pedro is still the leader in my opinion, because well, my
  opinion has a strong “opinion” that starters impact the game in a greater
  manner than relievers.  No disrespect to Rivera, perhaps the greatest reliever
  of all time.  So Pedro has benefited from being injured during much of
  the last three seasons, or perhaps not benefited.  Martinez would
  undoubtedly like to have been healthier the past few seasons, because I
  would guess that he actually enjoys playing baseball, rather than
  trying to rehabilitate himself over and over again.  But it hasn’t
  worked out for him.  However, the fewer starts that he makes, the
  higher his ERA+ should be.  And that gives us a feeling that he never
  really declined to begin with. But his ERA+ is greater than any
  starter, ever.  6% better than Lefty Grove, who had it much easier in
  terms of opposing players (theory, not fact)(6 percent in regards to
  ERA+ is merely 6 numbers higher.  For example:  Pedro’s is 154, while
  Grove’s was 148).  So there is something to be said about having the
  highest/best “Adjusted ERA” of all time for a starting pitcher.  Seems pretty relevant to me. 
  His counting numbers are lacking when comparing him to the other
  pitchers on this list (mainly the bext three), however his rate stats are clearly the best. 
  Pedro is third ever in K/9.  Third best in K/BB, higher than any of the
  top four on this list.  Pedro holds two of the nine best seasons ever
  according to ERA+ (3 of the top 20)–and one of the other pitchers on
  this list can say the same thing, as far as “two of the top
  nine” I mean.  Pedro has finished with an ERA+ of 200 or greater in an
  incredible five seasons.  He was absolutely incredible at his peak, and
  has most likely been the best ever when at the top of his game ( I believe he has has been, but I didn’t want to say it as fact).  This
  matters.  Counting stats matter too, and the next four pitchers were
  great, both at their peaks, like Pedro.  But also great when counting
  up their career numbers.  But Pedro was THE BEST at HIS BEST.  So maybe
  he will trail in career “Win Shares,” but he would also be the pitcher
  that I would choose if I needed a starter to win the most important
  game of a season.  And if someone asked me who the best I ever saw was, then I would have to go with Pedro.

• Roger Clemens:  ERA+ 143:  Clemens definitely has a strong case
  to be number one.  And I am going to avoid the PED crap, since everyone
  seems partially-guilty, and no one is in the clear.  If I had to guess,
  I would guess that the other four were clean, at least from using
  steroids, but how do I really know?  Anyway, enough negativity. 
  Clemens is one of the greatest pitchers this game has ever seen.  And
  if someone thinks he is better than Pedro, then I won’t put up too much
  of a fight.  Although I would disagree with taking Clemens over Pedro
  in a Game 7.  Clemens’ “Adjusted ERA” is tied for tenth all time with
  none other than Brandon Webb.  Obviously, Webb’s will come down over
  time, because I am pretty sure that Webb isn’t the same caliber of
  pitcher over the long haul, although great in his own way.  Clemens has seven Cy Youngs and an MVP. 
  Pretty remarkable, especially a pitcher winning an MVP (times have changed).  But Clemens
  was probably worthy of it, although not too long ago someone was
  arguing that statistically, Donnie Baseball deserved it more (I believe
  that it was Joe Posnanski arguing this).  But regardless, Clemens had
  an awesome season.  Clemens has three seasons of ERA+’s over 200.  And
  if no one understands, 200 is historically great.  There are far lower
  numbers that are considered great seasons for a pitcher, but 200 is
  just above and beyond them all.  Roger Clemens is perhaps the greatest
  pitcher of all time.  I might think Pedro,  but Clemens has a heck of a case
  too.   

• Randy Johnson:  ERA+  137:  Randy Johnson’s career is probably
  going to be remembered by many for his lack of success in New York.  A
  few problems with that:  One being the fact that Johnson was 41 during
  his first year in the “Big Apple.”  How many pitchers are great at the
  age of 41?  It was unrealistic to think that he could continue to be
  dominant at that age.  Plus, he wasn’t terrible, but average during his
  time there.  The other problem is that it is simply unfair to remember
  only two seasons in media-market hell (when you are playing below
  expectations).  Randy Johnson won five “Cy’s” in parts of 17 seasons up
  until his “struggles” in New York.  And the guy is still pitching well
  at age 44, and maybe at age 45 (2009).  But I mentioned that Pedro was
  third ever in K/9.  Well, guess who was first?  “The Big Unit,” that’s
  who.  The best K/9, ever.  EVER!  Since K’s best resemble what we think
  of as dominance, then Randy Johnson is just about as dominant as they
  come.  His postseason numbers are a little less appealing to the eye than his regular
  season numbers, but that is in part due to his forgettable years in New York. 

• Greg Maddux:  ERA+ 132:  Maddux was the other pitcher with two of
  the top nine ERA+ seasons of all time, along with Pedro.  Maddux was
  more reliant on his defense, way more than the other pitchers.  But he
  did not beat himself, walking very, very few batters each season. 
  Maddux walked only 20 batters in 33 starts back in 1997, which is
  almost unheard of.  And although he relied on his defense more so than
  the other pitchers listed, he may have had more control on balls in
  play than any pitcher that has ever lived.  If I needed one of these
  pitchers to be my pitching coach, Maddux would definitely get the nod.  At one point Maddux won four consecutive “Cy Youngs,” which is truly incredible if you think about it.  Actually those
  were the only four he won, but he was great in the surrounding years as
  well.  The durability that he displayed was amazing too, missing
  just a few starts over his entire career.  And that includes the part
  of his career at the end there where he hovered around league average for the last three years or so. 

• Curt Schilling/John Smoltz:  ERA+ 127:  I have tried to separate
  the two of them, but it is just too difficult to do.  They have the
  exact same ERA+, they’ve pitched roughly the same number of innings,
  roughly the same number of K’s.  Schilling did walk fewer, and allow
  fewer baserunners.  But it is so close that I really can’t find much
  distinction between the two of them.  Both were really great in the
  postseason, etc.  I find it hard to believe to find two pitchers with
  more closely related numbers than the two of these guys.  

And let me tell you something, before I even reviewed the ERA+
leaderboard, I had already made up my mind on the order of this list. 
It just happens that they are in order of their “Adjusted ERA.”  But I
would totally understand if one values 2-4 more than they value Pedro. 
Like I said, I place a lot of emphasis on Pedro being the most dominant
pitcher at his peak.  That matters a lot to this man.  But the other
pitchers careers extended much longer, and they had to sustain normal
declines (well, some did  :), something that Pedro hasn’t experienced, and may never REALLY
experience.  Although I very much cheer for him to put together a full
season again, to see how he can do with diminished stuff.