I use the Navigon app and personally I like it a lot. The motorcycle algorithm is definitely pointed towards more curvy roads and takes travel time less into account. The feature I like the most is that it shows you representations of the road and signs when you are on the highway so you can be in exactly the lane you need to be in and know what sign to look for. Not as useful on the bike but it's saved my ass a few times driving around downtown Atlanta. None of the apps allow a whole lot of route planning but for a-b directions Navigon gets my vote.
Sort of a side topic but with the right bluetooth set on your helmet, and Siri on an iPhone, you can pretty much do everything without ever touching the phone. You can answer calls, listen and respond to texts, listen to and control music, put in new directions, and pretty much anything else.