I'm making this post to note some of the differences I've noticed between the two apps when using offline mode. Let me know if you find any other differences I might have missed.

Things that Apple Maps does that Google doesn't:

• Walking and Public Transport routes.
• Location details (Opening Hours, Phone Number, Ratings,…) only if cached on device, otherwise it won’t show anything other than the location.

Things that Google Maps does that Apple doesn’t:

• Show phone numbers for all businesses (no need to be cached from what I can tell).
• Less storage occupied for around the same location/area downloaded.