Most of his skills not nin, but tai\nin. Which mean that you need to raise nin and tai both. Better nin.

You see, you need to raise or nin or tai - both will be good. Which one better depends on Naruto stats. Without any equipment - nin is better. But most likely those tops have much higher tai.

With equipment of course. You see if tai (not starter tai, but overall on char) is higher then nin, it's more logical for THEM to raise tai. Even if raising nin will give more stats. But there is almost no difference beatween tai and nin. 100-150 points.