Honorable mention: Alex Ochoa, Paul Janish, Don Werner, Juan Castro
5. Mariano Duncan (1.6 WAR)
Duncan was the team's starting 2B in the 1990 season, which was by far his best season in Cincinnati. He hit .306/.345/.476 that year, and led the league in triples with 11. He spent 1989 to 1991 with the Reds, but started his career in LA and played for a few other teams after Cincinnati.
4. Andy Seminick (5.0 WAR)
Seminick was a catcher for the Reds from 1952 to 1955. He spent most of his career with the Phillies, but put together some good years in Cincinnati in his early 30s.
3. Kevin Mitchell (7.8 WAR)
Batman had his best years with the Giants, but spent 2.5 good seasons in Cincinnati from 1993 to 1996. His 1994 was his best, where he hit .326/.429/.681 with 30 dingers and didn't even make the All-Star team.
2. Smoky Burgess (8.0 WAR)
Another catcher from the Redlegs era, Burgess was a little bit more famous. He make 5 All-Star teams with teams that weren't the Reds, but played in almost 400 games in his 4 seasons in Cincinnati. He had a .919 OPS in '57 (in 205 AB), which makes me wonder why he didn't play in more games than Ed Bailey, but I'll leave the Redlegs era playing time discussions for another day.
1. Ray "Iron Man" Mueller (10.1 WAR)
Mueller was another catcher, playing with the team from 1943 to 1949 (with a season spent in the service). They called him Iron Man because he caught every single game of the Reds' 1944 season, and set an NL record at the time by catching 233 consecutive games.
He wasn't too shabby, either. He got MVP votes 3 times, and finished 7th in the race in that 1944 season, the only year he made the All-Star team too. He hit .286/.353/.398 that year, on a team that won 89 games but finished 3rd in the NL.