Just into mastery to start, unless you plan to use magi then youd do mastery first with minimal investment in skele, but magi arent that good

And the difference between which one you max first is minimal

wait, u mean I should max skeleton mastery before I max raise skeleton? then I can only have 1 skeleton fighting for me?

My bad, I meant to say max skele first with 1 mastery
Unless you want to use magi also, then you would get 3 skele and then level up mastery

The trade off is fairly even, maxing skeleton first is slightly better