So I was thinking about cows. Obviously. And I got to thinking that maybe weaker animals could be more appealing choices for companions if they had bonus feats:
-Cow
Bonus Feat: Brew Potion
-Goose
Bonus Feat: Rage (monster ability)
-Mouse
Bonus Feat: Stealthy
-Canary
Bonus Feat: Resist Poison
-Alley Cat
Bonus Feat: Uncanny Dodge II