Nokia Here Drive+ uses the same maps (navitel) and speed limit database as Garmin. This makes it superior, in my opinion, as those are the most accurate. Navigon uses the same databases as Garmin as well, but doesn't offer any significant benefit over Nokia's offering. In fact, Nokia's is better in my opinion. CoPilot has outdated maps, maps that are just plain wrong, and the speed limit database is very sparse.
To me, the only two options are Here Drive+ and Navigon... and only Navigon if you don't have a Nokia.
I'm a very picky GPS user, and only use offline GPS apps.