this link is quite useful:
they show what skills you gain from reborn.
When you choosing what to reborn into you should be thinking what skills do i want.
So Since you are ninja, your skills are pretty much screwed already since you will only keep toxic fog when you reborn (unless you reborn into another ninja).
You have to decide what skills you want for your 2nd reborn.
I personally like war reborn into another war as you get reflect.
So I would say
ninja - warrior - warrior