After using Sprint Nav for years, its done its job well and took me to my destination. It always ran better on my BB than on android, but its always been a tad slow. It takes forever to get a gps signal, to reroute, and runs slow in general.
Now that my Hero is at its 2.1 stage, Ive been using Google Nav exclusively. I like the features, its fast, and it reroutes almost instantly if you take a different turn than directed. The street view of your destination at the end is a nice touch along with the darkened night view.
Google also can let you touch any point on the map and itll give you directions to it, something Sprint cant do. It just needs to be polished a bit more and itll become the king of navigation.
To me, the Google Nav girl is easier on the ears and pronounces streets better than the Sprint girl.