I mean, obviously it's 1991 (before my time). I mean, it would be trolling to say otherwise.
But what is No. 2?
I'd argue (as I've done before) that it's 2006, and not 2004 (which everybody seems to like).
1. Cal won a co-Pac-12 championship in 2006, the only Cal football championship in Justin Wilcox's lifetime.
2. Cal won the bowl game against a tough highly regarded arrogant opponent, which set up the greatness of the next (first half) of the 2007 season (while the 2004 team lost to a tough highly regarded arrogant opponent).
3. Cal had the Pac-12 offensive and defensive players of the year (Marshawn and Dante Hughes).
4. Cal had a tougher Pac-10 schedule in 2006 having to play 9 teams and going 7-2, which is more challenging than playing 8 teams and going 7-1.
5. Tougher OOC schedule: 2 Power 5 teams in 2006 vs. 0 Power 5 teams in 2004.
6. Tougher schedule, period. Playing 13 games in 2006 vs. Playing 12 in 2004.
7. 3-2 vs. ranked teams in 2006 vs. 1-2 vs. ranked teams in 2004.
8. 2 legendary wins in 2006 (destroying a ranked Oregon and a ranked Texas A&M) vs. 0 legendary wins in 2004.
9. The best win in 2006 is actually a win. The best "win" in 2004 is actually a loss (USC).
10. 2006 Cal players earned 3 rings from their season.