sacrifice B or N?

If you need to choose between sacrificing a B or N - which should one choose?

(assuming there is not some additional clear advantage in position with one or the other, etc.)

Well - is it really meaningless since B can only attack their own colored squares while the N can move and attack any color sq.

I'm a beginner so not arguing this - but maybe the gist of my question is clearer.

There is no rule...When you "sacrifice" material, you should be doing it for some clear gain.  If there is no clear gain, you shouldn't be sacrificing material.  If you have a choice between sacrificing a knight or a bishop, do whichever one you calculate to be better.  Material sacrifice is a tactical problem; your question is a position question.

BOTH

Not always.