Which mode uses the least battery? The docs don't say much at all about the modes.
Some background is that they all result in location updates every 1s, I would gladly trade battery performance for less frequent updates.
It's difficult to say.
What are you using it for? If it doesn't fall into one of the listed modes, I would use default and expect the OS to do the right thing.
Which mode uses the least battery?
I think they are all probably very similar; they all use the same hardware, but do different software processing of the results IIUC.
I would gladly trade battery performance for less frequent updates.
My understanding of how the GPS hardware works is that the radio needs to be continuously on, whatever the update rate. Unless you want very infrequent updates, e.g. every ten minutes or less?, the energy cost is much the same. Maybe.
I would use default and expect the OS to do the right thing.
You might be disappointed. For example, “default” snaps to where Apple Maps thinks road centerlines are.