I bought Sygic, Navigon and TomTom.
Out of these, the weakest is Navigon, which I had no hesitation returning. It doers not warn users for overspeeding, does not contain speed for any of the roads in Metorpolitan Sydney, Has no red light camera or speed camera warning, has no school zone warning, has no proper trip simulation, and has the most difficulties with GPS signal among the tree. For Navigon, I emailed Navigion and copied the email to iTune support and got my refund back.
TomTom was the second return. It does not provide audio overspeeding warning, and does not warn us when approaching a school - both of these weaknesses were the deal breakers. TomTom has no email contact for iPhone on their website, so I just emailed iTune and got the refund.
Sygic has the best functions and features of all the three I've tried, being the only one that can provide audio and visual overspeeding warning, red light camera warning, speed camera warning, trip simulation, and warn when approaching schools. It has the winmo style of interface, which is its only weakness.
99.9% of the time when I use a GPS, it is not to tell me how to get to a destination, but to provide warning against inadvertant overspeeding, when approaching a school, and traffic cameras. Sygic is the only candidate in Australia that is capable of these functions and features. Not Navigon. Not TomTom.