I use the Navigation that is included as part of Google Maps on the Android. The 'pros' include, free, maps seems to be much more current that 'manufacturer' maps, and for the past 2+ years has worked well for me.
The "cons"; you must start a route with a decent data connection! If you do not have a data connection when setting the route, you cannot get turn-by-turn audio directions. Also, you may need to position the smartphone, such that it does not overheat.
When I upgraded to the Droid 3, I kept my OG Droid. I set it to airplane mode and turned on GPS and WiFi. I installed the 'free' version of the app 'Navigation" by TeleNav. This app does not require a data connection. I have used it around Richmond, VA and it seems to work well. I have not had an opportunity to use it on a trip of any length. Pros, does not require a data connection; cons; maps are not updated as frequently as Google maps.
I recommend using the the Navigation via Google Maps that came with you phone.!
Bob