This one is a no-brainer. Jerry Dipoto, who is now the GM of the Seattle Mariners, wore 45 for the Rockies and has arguably had the more successful post-playing career.
Scott Oberg wears the number currently on the team and, with Adam Ottavino gone, he has been the most consistent arm coming out of the bullpen. However, the greatest player to wear 45 for the Rockies is Jhoulys Chacin. The righty spent six seasons of his career with the Rockies. After Ubaldo Jimenez left for the Cleveland Indians in 2011, he became a mainstay in the rotation alongside Jorge De La Rosa.
For several years, he pitched consistently with a sub 4.00 ERA, having his best season in 2013 with 14 wins, 197 innings, and a 3.47 ERA. By 2015, he lost his effectiveness and was released in spring training.
He has made a lengthy career bouncing around to other teams and eventually pitched against the Rockies in the 2018 NLDS against Tyler Anderson. In a game Rockies fans would soon like to forget, Chacin threw a shutout over five innings, getting the win.
In the offseason, Chacin signed a minor league contract with the Minnesota Twins.
Jason Hammel wore the number 46 the most in Rockies history and he mostly wins this by default.
Before Hammel came to Denver, he was on the Tampa Bay Rays squad that made their first run to the World Series. The Rockies only gave up a pitching prospect that never played for the Rays in Aneury Rodriguez.
In three years with the Rockies, Hammel had a 4.63 ERA with a 33-22 record. He became an effective middle of the rotation arm. Even though the Rockies lost, he started Game 3 of the 2009 NLDS where the Rockies led in the late innings.
By the way, I’m still convinced the Phillies stole those last two games in Denver. But that’s for another conversation.
Hammel was traded to the Baltimore Orioles for Jeremy Guthrie, which, in retrospect, was one of the worst trades in franchise history. Hammel wasn’t amazing in Baltimore with a 15-14 record and 4.27 ERA, but Guthrie didn’t even finish the year in Denver being traded to the Royals after posting a 3-9 record with a 6.35 ERA.
That basically summed up the 2012 season, which was the worst, based on wins, in franchise history. “The Rockies should have kept Hammel” is an understatement.