Here's my list, determined by winning percentage against the "first division":
AL East: 1936 Yankees, 1946 Red Sox, 1969 Orioles, 1986 Blue Jays, 2010 Rays
AL Central: 1995 Indians, 1917 White Sox, 1934 Tigers, 1930 Senators, 1989 Royals
AL West: 2001 Mariners, 1910 (Philadelphia) Athletics, 2008 Angels, 1986 Astros, 1999 Rangers
NL East: 1958 (Milwaukee) Braves, 1988 Mets, 2010 Phillies, 1997 Marlins, 2012 Nationals
NL Central: 1906 Cubs, 1902 Pirates, 1946 Cardinals, 1940 Reds, 1982 Brewers
NL West: 1913 (New York) Giants, 1951 (Brooklyn) Dodgers, 2007 Rockies, 1998 Padres, 2002 Diamondbacks
Notes:
- The strongest team is the 1906 Cubs. The weakest team is the 2012 Nationals.
The NL Central is by far the strongest division, containing two strong early 1900s teams and two other top-10 teams.
The NL West is the weakest division, with their strongest team being the 101-51 1913 Giants and containing three of the four weakest teams.
The strongest team that didn't make the cut is the 1942 Cardinals. The strongest non-WW2 team that didn't make the cut is the 1932 Yankees.
If teams must be in their current city to be eligible, the teams that have since relocated are replaced with the 1988 Athletics, 1999 Braves, 1991 Dodgers, 1962 Giants, and 1970 Twins.
If strike-year teams are eligible, the 1994 Royals and 1994 Expos make it in.
If the Expos and Nationals are separate, the 1996 Expos make it in.