Both, or sometimes not both, it depends.
I use a Lee collet die to size the neck and then a Redding body die to size the body and "bump" the shoulder about 0.002.
Competitive shooters (top level) all full-length size their cases.
For convenience and because in a factory gun with a good but not exceptional shooter it really doesn't matter, I often neck size only.
Still happily answering to the call-sign Peetza.
The problem, as you so eloquently put it, is choice.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.