Number 2–Aaron Cook (17.1 bWAR, 17.3 fWAR, part of 10 seasons as a Rockie)
Aaron Cook is the longest-tenured starting pitcher in Colorado Rockies history so, naturally, he made himself on to this list, partially due to that fact.
However, he was still a key cog in the Rockies rotation during that decade. In his Rockies career, he went 72-68 with an ERA of 4.53, an ERA+ of 106, and a FIP of 4.39. Cook was an extreme ground-ball pitcher as his groundball rate was north of 60 percent and his strikeout rate was only 3.8 per nine innings, which is half or less than half than most pitchers currently.
He is second to De La Rosa in all-time wins as a Rockie, 4th in walk-rate per nine innings, the all-time leader in innings pitched, games started, and second in complete games.
His best season came in 2008 when he was an All-Star. He went 16-9 with an ERA of 3.96 in 32 starts (211 1/3 innings). He had an ERA+ of 118, a FIP of 3.76. His walk rate and strikeout rates were better than any other point in his career at that point and his home-run rate was the lowest that it had been since 2003.
Honorable Mentions
The Rockies have some guys that could eventually be in, or top, this list in a few short seasons. Chiefly, Jon Gray is very close to making this list as it is. If not for his 2018 season, he would be on this list. Kyle Freeland could also be on this list soon if he can return to his 2018 glory.
Other than those two, Pedro Astacio, Jeff Francis, and Jason Jennings were the closest to making the list.