Number 4–Jhoulys Chacin (14.7 bWAR, 9.9 fWAR, part of six seasons as a Rockie)
Record-wise, Jhoulys Chacin would not make this list as his record was 38-48 in 124 games (109 starts) as a Rockie. His other numbers show that he was a victim of poor run support from the Rockies offense.
He pitched to a 3.78 ERA with an ERA+ of 120. He also had a FIP of 4.03 and he had a WHIP of 1.338.
His best seasons were in 2010-11 and 2013. In 2010, he went 9-11 with a 3.28 ERA in 28 games (21 starts). He had a FIP of 3.55, a 9:4 strikeout-to-walk ratio, a WHIP of 1.274, and an ERA+ of 142. In 2011, he added ten more starts and nearly sixty innings to his 2010 total when he went 11-14 in 31 starts. His ERA was 3.62 (4.23 FIP and an ERA+ of 126).
He was injured in 2012 so he only had 12 starts but he was excellent again in 2013 when he went 14-10 in 31 starts (197 1/3 innings). He had an ERA of 3.47 with a FIP of the exact same and an ERA+ of 129.
Number 3–Jorge De La Rosa (15.5 bWAR, 15.0 fWAR, part of nine seasons as a Rockie)
Jorge De La Rosa is, without question, the best left-handed starting pitcher in Colorado Rockies history.
In his Rockies career, he went 86-61 with an ERA of 4.35 in 209 games (200 starts). His FIP was 4.24, and his WHIP of 1.381. Those 200 starts are second in Rockies history, only behind the guy who is next on the list and he is the Rockies all-time leader in strikeouts with 985, more than 200 more than the next person (who is also later on in this list). He is also the Rockies all-time leader in wins.
His best season came in 2013 when he went 16-6 in 30 starts. He had an ERA of 3.49, an ERA+ of 128, and a FIP of 3.76.