The best alternative to google maps is still "Here" (recently rebranded to "Here We Go" which I guess is the best they could come up with to salvage the existing bass-ackwards name without changing it altogether). https://play.google.com/store/apps/details?id=com.here.app.maps https://en.wikipedia.org/wiki/Here_WeGo
Here's scheme allows the entire US & Canada (or individual states/provinces) to be downloaded and stored locally, and the app itself can be put into an "offline mode" which limits POI searches, but works fine for mapping & navigating to addresses. In this respect, it is very similar to CoPilot.
Unfortunately Here stopped making the "hi-fi" (TTS street names) voices available some time ago, and the "standard quality" voices are markedly inferior to google nav's excellent voice directions. Last time I updated Here, it still worked OK with the old Hi-Fi voices, but unless you downloaded when they were available (or know somebody who did, like me), then you're SOL. In this blog post
, some commenters revealed that the old Hi-Fi voice files still work, and provided links for users to get them, but Here put an end to that, saying they don't "support" those much better Hi-Fi voices. Read some of the latest comments on that post, and you can see how frustrated users are about having Here try to force this retrograde step.
Here really screwed the pooch on this one, even as google nav's voice directions have steadily gotten better. IMO, great voice directions are one of the most important functions, because it allows the driver to keep his eyes on the road.
That's not Here's only screw up. As the comments to this blog post
attest, Here has yet to provide any way to use here.com to plan routes that are seamlessly accessible on a mobile device. They screwed this one up even worse than google, which does not come close to what S&T had a decade ago.
Here was bought by a consortium of automakers, who may be moving toward with-holding the best and most useful features from a free Android app, and making them available only in their in-car version.
A couple years ago, I extensively tested most of the other alternatives, including mainstream products like Navigon and TomTom's Android app, along with less well-known contenders, like Sygic and some others I don't even remember off the top of my head. Most in that last group just outright stank. Navigon and TomTom were OK, but certainly a big step down from google maps for local search, and not as good as google's current voice guidance either. Both Navigon and TomTom had some pretty big limitations in their interfaces too, I guess due in part to their standalone PND heritage. A lot of little things you'd take for granted as being a breeze in google maps were quite a chore in either one of those.
FWIW, the current version of the Android google maps/nav app does allow large maps to be stored locally, although they try to update automatically via WiFi every 30 days. I'm not sure if the existing local maps keep working if the update is not successful.