I use Garmin. The incentive for me was the ability to pay a one time fee, which pays for itself after ten months. I've found it pretty easy to use and reliable. I haven't used anything else, so it's hard to compare.
I actually like the built-in Blackberry Maps for navigating. It works just fine for me. I don't need to have my map shown to me in 3D. The map will continually update your position while rotating the map correctly to your driving direction like it should (a MUCH NEEDED feature in google maps).
I found the mobile Garmin product satisfactory . My entire family has had Telenav’s service for the past 2-3 years, and we will never switch. Telenav includes the free real-time map updates, traffic/weather updates, POI updates, among other things.