Hello, I search all the existing means to maximize Aid another action (Attack, AC, Skill, saving throw) :
traits, feats, classes, PrCs ...
Thanks for your future help.
Helpful halfing doubles Aid Another. You must be a halfing, or you must also take the adopted trait.
As Magyc said, the halfling race trait Helpful (from pg. 30 of Halflings of Golarion) is a good option. Another good option is a cavalier of the order of the dragon (from pg. 35 of the APG), with the Aid Allies order ability; it starts off lower than Helpful, but is higher by 14th level. Please note that Helpful and Aid Allies do not appear to stack, since they both replace the usual +2 bonus instead of adding to it.
Battle herald PRC adds a bonus if you take the teamwork command