Best Navigational GPS Client?

[Temujin]

As I browse through the threads, I see people throwing around, iGo8, Garmin XT, TomTom, Google Navigator, etc.

What are the pros and cons of each?
Ease of Installation (memory card or internal memory?):
Primer necessary? (which one's best?):
Voice quality/street name pronunciation?:
Efficient route planning (short roads, speeds, traffic planning, etc).
Visuals: Size of arrow, legibility of street names, etc
Any other miscellaneous comments:

I certainly believe this will make my decision less difficult and hopefully assist any others struggling with the same question.