Kallard has the highest strenght, constitution and height which gives you the most HP and damage bonus of any human race. They are the biggest hardest hitting humans, but also slowest (96 dex). They are the “thursars” of the human races.
Sidoian also have 105 strength but they are not as tall so not as much damage bonus or hp. They have a lot more intelligence than Kallards. Much more geared towards a slow, beefy mage.
Tindreme have less strength and Con, but more dex. Its a more balanced, all around type of build. Only Khurite are faster.
It all depends what you are trying to make. Each human race has its strengths. The human clades are very useful for melee as, one acts like a purify (removes magic effects), and the other lets you resist spells for a short time. Very good when fighting a mage.