I've noticed the familiars who are non-favorites tend to have high stats, higher max levels, and more powerful spells.
To be honest, I didn't really notice a difference between the familiars who gained the 10% favorite bonus and the ones who didn't. I just trained familiars I liked and tried to balance my party with tank, dps, and healer for each character.
do they have extra stats to compensate for the fact that they don't get the increased 10% stat bonuses? auralynx is the only one i can think of, right off the top of my head.
or are they just there to offer more choice? i'm looking for a healer/support for oliver and i'm having troubling finding one within his preferred genuses.
I feel like a lot of the Arcana Familiars are actually pretty good. They don't get the 10% bonus, and perhaps that so they could be used interchangeably between characters. The Auralynx is cool, but you don't get it till late. The Kipper is good at putting things to sleep, and I used Hullaloon the entire game.