Castillo has been inconsistent. Gray struggled through much of 2016-18. Bauer has only been great one season and was brutal for the Reds last year (6.39 ERA in 10 starts) after they acquired him. We mentioned Miley’s struggles late last year. DeSclafani has been inconsistent as well, though with him slotted as a five he’s the most sure bet on here. The odds of him pitching better than a run-of-the-mill fifth starter are pretty good. 
Thanks to a fruitful last few years in grabbing rotation help on the cheap, the Reds appear to have filled out a nice rotation heading to 2020. 
Further, Miley had great success in the NL Central in 2018 with the Brewers, thanks in part to his newfound reliance on a cutter. In 16 starts for the Brewers, he was 5-2 with a 2.57 ERA and 1.22 WHIP. He only gave up two earned runs in 14 2/3 postseason innings that season, too. Of particular note here is that Derek Johnson was the Brewers’ pitching coach that season and he’s now the Reds’ pitching coach. 
Here’s how it stands: 
The Cincinnati Reds have agreed to sign left-handed starting pitcher Wade Miley to a two-year, million deal with a club option for a third year, reports Mark Feinsand of MLB.com

  1. Luis Castillo, RHP
  2. Sonny Gray, RHP
  3. Trevor Bauer, RHP
  4. Wade Miley, LHP
  5. Anthony DeSclafani, RHP

If they get the good version of those five guys, it’s a formidable rotation that could shoot the Reds into the playoffs. 
There are some possible pratfalls, though.
In all, this is a nice move by the Reds as they look to jump back into contention on a hard-to-read NL Central. 
Miley, 33, had an up-and-down 2019 season for the Astros. Overall, he was 14-6 with a 3.98 ERA, 1.35 WHIP and 140 strikeouts in 167 1/3 innings. Of course, he had a 3.06 ERA through August and looked like he would be a fixture in the Astros’ playoff rotation. Instead, he pitched to a 16.68 ERA in five September starts and fell out of favor. Still, he was good for most of the season.