They recently allowed offline maps. And the good news is that the direction works offline as well.Google maps need active data plan, HERE map doesn't. Will work without even a SIM worldwide.
I have used a couple GPS including, Here on Nokia and Here on Android, Garmin Nuvi, Tomtom Android, and a few more. (I use Ovi Maps as well if anyone remember it from old Symbian days).
None of them are perfect but most of them are workable. They all have improved a lot in past few years and for just directions I guess they are all very close. I think an independent GPS still has slight edge over mobile but I guess soon they will be identical. The difference maker will be traffic and not
Garmin pros are,
direction on left or right, Up ahead (search restaurants, ATM, petrol while in drive on the route)
Cons -> Do not auto reroute if there is a faster route available (Google does it)
Android Here Maps: Best offline maps application till google was just online. Does not tell if the destination is on the right or left. Do not auto reroute based on traffic.
On long drive I used Garmin which has HD traffic receiver with Google Maps (for alternate traffic), primary use of Google is its integration with various traffic services and it helps to have an alternate map/traffic solution just in case. Though I used here maps a lot I think for traffic I will rate google maps to be better. Plus I use maps.google.com a lot and I can just sync it easily.