If you're interested in traffic avoidance, the best data comes from Tomtom. It's theoretically capable of detecting congestion on over 99% of roads and I've seen enough to confirm that this works the majortiy of the time. Every other traffic service I've used has been a case of hit and miss. Tomtom is way out in front for both traffic and routing.
Route 66 Navigate use the Tomtom map and traffic data and have a free trial for 30 days. The routing is usually very sensible. I would highly recommend giving it a look. If you do decide to buy, it's cheaper than Tomtom's own app. If you set the traffic avoidance to automatic, redirection is obvious but entirely hands free. On the occasions when the traffic data doesn't pick up incidents it also has a feature to manually block certain roads.
Google Navigation is continually improving but Tomtom still picks up traffic on roads where Google never detects it. Google's advantage is up-to-date mapping (Route 66 updates are twice a year) and far better search plus OS integration.
As well as those two, I've used Waze, Navigon, Navfree, Sygic, Tomtom, Copilot, M8 and others. Route 66 and Google Navigation really are top of the pile but they both have their advantages and disadvantages.
I short, if I could have a satnav app that did everything well, I'd probably go for:
- OS integration, search function and map update frequency from Google
- Voice directions and TTS traffic reports from Navigon (if you wanted entirely audio driven directions it's brilliant)
- Live Traffic data from Tomtom (and Route 66 Navigate - it's the same)
- Routing from Route 66 Navigate
- Graphics from Sygic
- Route planning and modifications system from copilot
Edit: Tomtom do have their own android app, which is just not as slick as Route 66 Navigate and is more expensive. They will also be launching a new app, Tomtom Go, soon. This will be based on a freemium model - so you get about 70km a month navigation and traffic etc free a month. Over that you need to pay. Tomtom Go is currently only available in Italy but should launch worldwide soon.