Whos betta? i cant decide

Depends on what you want. Tau are best for shooty shooty type armies, and Kroot like mele a bit more and can soak wounds better. Generally a mix is best, but if you were to choose fielding an army of one or the other Tau is generally the best choice from what I hear. This would probably be because they get generally better or at lease more options on what to field. Plus Kroot really are for jungle fighting.

As said, depends if you want a melee or long range army. But Tau is the best choice imo.. most armies have better melee than Kroot anyway.

The only reason to have kroot in a TT army is for the ability to soak up ammo and leave your Fire Warriors alive long enough to shoot off their strength 5 plasma rifle with targeting.