Both are Good but...
Google navigation launches much faster and is much easier to get through the screens. Google Nav also shows a picture of the destination, which is really good for locating a house, and Google Nav has a better sync feature for your contacts and other Google applications. Sprint Navigation is much slower to launch, and has been unable to sync with my contacts' addresses from my Samsung Moment. However, the on screen display of the navigation on Sprint Nav is much better. It gives you a 3D car icon and looks like stand alone GPS displays. Also, Sprint Nav allows you to save your location, search for gas by price, etc. Sprint Nav has way more features. The thing that takes the cake is that Sprint Nav's Voice-over is much easier to understand making it more usable than Google Nav. However, Google Nav shows a lot of promise and may overtake Sprint Nav when it gets an update, which is more likely that Sprint Nav getting an update. So, Sprint Nav wins for me now, but Google Nav can catch up with some updates. Hey, when I first launched Google Nav, it said it was still in beta! It could get much better.