When I'm navigating to a specific place, it makes the most sense to zoom based on the distance to the next turn because it makes a visual reminder for the turn coming up and shows the most detail. If I just have waze open, however, it doesn't know when I'm turning, so it should zoom based on speed. I realize not everyone may want this, however, so make 2 categories of zoom options: choose how you want it to zoom when navigating and how how you want it to zoom when just driving.