Below are the classification All Stars for the NL Central as provided by Baseball America. These are not necessarily the top prospects at each classification but they are players who performed the best over their time in that classification.
Fernando Kelli OF (Dominican) - The fact you have to go as far down as the Dominican summer league to find an All Star tells a lot about the Cubs minor league system. Speed appears to be the best tool in his game with 58 stolen bases in 67 games. He also got on base with a .327 average and a .437 OBA. He does seem to swing and miss a lot, not what you want to see in a lead off hitter and his power is limited to the gaps.
Tyler Mahle SP (AA) - The seventh round pick threw no hitters in 2016 and 2017. His fastball can hit the mid-90s but is not overpowering. He relies more on mixing in his secondary pitches (curve, slider and change) to complement the fastball. Between AAA and AA he limited the opposition to a .208 average. They hit him a little better when promoted for four starts in the major leagues (.253) and his control of the strike zone was a bit shaky (11 walks in 20 innings) but his ERA was good (2.70).
Jose Siri OF (Low A) - There is a lot of raw power in his bat (24 homeruns) and his legs can steal bases (46). That speed allows him to cover a ton of ground in the outfield. His arm is strong leading to the possibility of a five tool athlete if he can develop. His only downside is his patience at the plate (33/130) with a tendency to swing and miss too much.
Taylor Trammell OF (Low A) - A two sport athlete in high school you can count the same tools for Taylor with Jose. He showed speed with 41 stolen bases and power (13 homeruns). Taylor has better patience at the plate (71 walks) with the speed to cover center. His arm is not as strong as Siri so when not playing center he fits better in left.
Debby Santana 3B (Dominican) - He was the youngest player on the Dominican All Star team (16 years). The power is limited to the gaps but as he matures many of those balls will carry over the fence.
Lewis Brinson OF (AAA) - Drafted by the Rangers in the first round of the 2012 draft, the Brewers acquired him in the Jonathan Lucroy trade. The speed and power exist for him to be a 30/30 player, though his stolen base numbers were not high last year. He struggled when called up by the Brewers (.106), but he should be the centerfielder of the future for the Brewers.
Corbin Burnes SP (AA) - The fourth round 2016 pick does not rely on power, with a fastball that can hit the mid-90s but often sits in the low 90s. His slider gives him a good swing and miss pitch to complement his fastball. He needs to develop his change or move to the pen. The opposition hit him at a .212 clip and he showed good command of his pitches only walking 20 in 86 innings.
Nate Griep (High A) RP - Nate picked up 30 saves but bullpen pitchers with low strikeout rates (7.5 per nine innings) are not commodities to get excited about. He did limit the opposition to a .191 average so there was a lot of soft contact with his offerings.
Jean Carlos Carmona SS (Dominican) - He hit .302 but with very little power and no stolen base speed. Myworld anticipates that he carries a good glove but we don’t have much info on him.
Steven Brault SP (AAA) - The Orioles have traded a number of mid-rotation pitchers to keep their playoff hopes alive. Brault is another one of those pitchers that fits on the cusp of being mid to back rotation pitcher. He throws lefthanded relying on breaking pitches to retire hitters. Minor league hitters struggled with a .199 opposition average, major league hitters juiced him at a .287 average. He might be best used out of the pen as an emergency starter.
Luis Escobar SP (Low A) - At 6′1″ he is small, but his fastball has easy mid-90s velocity. His command is a bit erratic but he has swing and miss stuff. He needs to enhance his secondary pitches (curve and change) to stay in the starting rotation.
Mason Martin DH (Rookie) - The 17th round 2017 pick opened some eyes with his 11 homeruns and .630 slugging. He also walked 32 times in 39 games for a .457 OBA. Mason played most of his games at first base but did see some time in the outfield.
Sherten Apostel DH (Dominican) - The Curacao native did show some pop with 9 dingers. He also had an impressive 56/49 walk to whiff ratio. This was his second season in the Dominican League and he made enough improvement to go stateside next year. He has played third base the last two seasons.
St. Louis Cardinals
Evan Mendoza 3B (short season) - The 11th round 2017 pick hit .370 in short season. When promoted to Low A it dropped 100 points. There is gap power but if he hopes to stick in the infield corner slot there needs to be more.
Scott Hurst OF (short season) - Hurst was a third round pick in 2017 but the first player the Cardinals selected in the draft. Speed is his best tool which allows him to play centerfield. There does not appear to be much power in his bat to play a corner.
Ivan Herrera C (Dominican) - The native of Panama carries a mean stick (.335). He also threw out 34 of the 85 runners who stole off him.