Seems to me, as a broad general proposition:

1) Consistent use of North up is better for longer-term navigation or
course planning, when you're zoomed out on the map and asking, "Where am
I in the big picture?" or "What course should I take to reach a given
(distant) destination?" (or to avoid things I should avoid).

Better chance of identifying major landmarks (lakes, mountain peaks)
correctly and understanding the broad situation.

2) Track up better for short-term maneuvering, when you're asking "What
should I be looking for, and what maneuver do I have to make, in the
next few minutes?"

I suppose optimum might be a rapid way to toggle between the two views
-- with (*very* important) some kind of obvious (and standard) visual
difference in the two views that will unmistakably clue you as to which
display mode you're in.