I will probably continue to use Apple Maps as map data is accurate where I live. Here are a few observations:
Google Maps german voice is very nice, less robotic. But it is less exact with pronounciation of street names. Sometimes it makes strange pauses, sometimes it is just a flow of words:
"In 400 meters...pause...pause...pause...turn left"
"turnleftonthisstreetthenturnrightontheotherstreet"
Directions are shown in lock screen, but only text, often pretty long, nothing I feel safe to read while driving. Speech and text don't come always at the same time, a little disturbing.
Battery usage is quite bad on both, but data usage is 250K (Apple) vs. 1.5M (Google) for the same route. Google didn't find a server in our underground garage (same with Apple sometimes) but even when I was already in full LTE coverage I still needed to try half a dozen times - on the Autobahn already
General look & feel is better on Apple's maps IMO with search being better on Google's (as expected).
When entering a new street, Apple already tells you about next exit (which I think is a nice touch), while Google just says how long to follow.
Navigation itself is accurate on both where I live, Route selection is a matter of taste (nice that Google shows alternatives, but taking traffic into account both seem to offer very good routes).
Google Maps offers me no transit directions, not even with walking a few kilometers or suggesting a taxi like the website does. I didn't hope for it as Google's data does not include our local busses and trams.
The company I work for is on Google's Maps, but not on Apple's, my home location actually has a few more and more accurate POIs on Apple while Google has some more important ones. Both of them are pretty outdated.
So apple has the slight edge for what I need, will use it mostly for the lower data usage. If you want more POIs, live in one of Apple's forsaken countries like the UK or need street view the choice is obvious anyway.
Now why all the years and billions spent by Apple to finally have a TBT version of Google Maps on iOS? Anyway, choice is great and Google sure has the easier task to get their solution to perfection, if they offer offline maps earlier than Apple I sure will use their maps more.