These are chronological.....
The Big Ten's iterations:
23 years of being 10 teams
10 years of being 9 teams
40 years of being 10 teams
21 years of being 11 teams
3 years of being 12 teams
7 years of being 14 teams
.
The SEC's iterations:
32 years of being 12 teams
2 years of being 11 teams
24 years of being 10 teams
21 years of being 12 teams
9 years of being 14 teams
.
The PAC's iterations (excluding some weirdness around 1960):
22 years of being 10 teams
9 years of being 9 teams
19 years of being 8 teams
33 years of being 10 teams
10 years of being 12 teams
.
Big 8/12 iterations:
19 years of being 6 teams
11 years of being 7 teams
38 years of being 8 teams
14 years of being 12 teams
10 years of being 10 teams
.
ACC iterations:
18 years of being 8 teams
12 years of being 7 teams
8 years of being 8 teams
13 years of being 9 teams
1 year of being 11 teams
8 years of being 12 teams
7 years of being 14 teams
.
SWC iterations:
31 years of being 7 teams
20 years of being 8 teams
20 years of being 9 teams
.
I figure the bolded ones are the "golden age" where we all fondly remember college football being perfect.
The B1G with MSU, the SEC pre-divisions, the PAC-10 w/ the Arizona schools, the original Big 8, the SWC w/ Houston, and the ACC w/ Florida St