iPhone6+ user here.
As a person that's extensively used both Google Maps and Apple Maps (to actually compare the two), Google Maps is superior in quite a few ways, though Apple *is* gaining. I'm not one to praise Google, but when they do something right, they deserve credit, and I hope Apple copies every last feature.
I'd say in about two years, Apple will have caught up and it will no longer matter.
That said, Google Maps does do quite a few things that are simply superior to Apple maps as they exist today.
1) Google Maps turn by turn tells you which lane to be in, while not a huge deal, it's nice, especially in big cities with complex highways.
2) Google Maps turn by turn does not lock you into a specific zoom radius or prevent you from rotating the map (and the map staying how you rotated it). Apple maps locks you into a very tight zoom radius AND prevents you from rotating the map, which is an annoying use case.
3) In Google Maps turn by turn, it still shows you traffic data, for some reason, once you go into turn by turn in Apple maps the traffic data is gone and you're driving "blind". I like to know if an area of congestion is coming even while in turn by turn.
4) Google Maps has 1 touch zoom, enough said. Double tap on Google Maps (holding on the second tap, move finger up/down to zoom in and out, it's simple and brilliant, especially with the larger phones which Apple now sells.
5) With Google Maps, I can make restaurant reservations right through the app, without the need to install additional apps OR sign up to use them. You can also call/reserve UBER rides AND book hotel rooms right through Google Maps, just as easily AND it tells you the current booking prices from a number of sources.
6) I don't use this, but Google Maps transit directions is much more comprehensive, though Apple should be catching up rather quickly.
7) Because Google Maps is not tied into the OS (which doesn't really add much in the way of functionality aside from "lock screen" directions), it's base map is updated much quicker. For example, in Chicago, Maggie Daley park still shows the old park layout in Apple maps, while in Google maps it's been updated to reflect the walking paths as they've now existed for 6 months. And when using turn by turn, Google Maps keeps your phone active, so the need for lock screen directions seems arbitrary anyway.
8) Until this week Google Maps lacked night mode, but it has that now, too...