QCar? ;-) But I am one of the creators, so do not take my word too seriously.
The pros and cons as we perceive them:
+ Extremely flexible thanks to plug-in architecture
+ Probably the most extensive function set (incl. navigation, mail reader etc. etc.)
+ Supports most hardware incl. special stuff like Phidgets, OBD etc.
- It seems to be quite difficult to configure for Mac folks, not used to text config files
- The GUI is efficient to use, but not as nicely looking as some other FEs
- Not completely open source - this might be seen as a problem by some
If you just want a front end for Mac-based in-car entertainment, QCar is probably too complicated and CFE or other front ends will do a better service.