Route 66 Navigate. Best combination of live traffic data and sensible routing and accurate ETAs for a reasonable price. I use it because more roads are covered by traffic info than Google and rerouting due to traffic is entirely hands free, automatic and usually reliable. When it comes to traffic information and routing algorithms I'm a bit of a geek, hence the number of apps I've tried just to see how they work.
Supplemented by Google maps / navigation as the search is superior and map updates more frequent than Route 66.
That's agains a background of having previously used: Tomtom, Sygic, Navigon, Copilot, Waze, Navfree, M8, Wisepilot and a few other random ones.
When it comes to Live traffic - Tomtom's traffic is the only one worth paying for. It's used by Tomtom, Route 66 and Sygic. The implementation is crap on Sygic, however, so I don't recommend it. Next best is Google which is free, then Waze (also free). Hence all the other apps' live traffic info is not worth paying for.