Good Map Data
It's very important to know that good map data quality will make or break a navigation system. A good map data provider will provide planned updates and also customer support in terms of getting feedbacks and working on consumer's suggestions or complains
Sensitive GPS
A sensitive GPS receiver is upmost important for any navigation system. It must be fast in getting fix (Time to fix) and also durable, precise and accurate.
Ease Of Use
The best criteria for any products is of course, Ease of Use. A good navigation system must not only looks good but be easy to use and able to share the good experience with others.