As a truck driver I spend most my life using SatNav's on UK and European Roads.
I would highly recommend the NavFree one, its just as good as anything else out there and its free. It will always get you to where you want to go, and thats about all you can ask. I also prefer its routing and speed to the TomTom apps. I used it exclusively on my iPhone for well over a year and it just works.
If you want to pay for a solution, then I'd say Copilot are the best, very very fast fixes, fast app time, great routes and nice clear display and information, as well. BUT.....
Go for the Renault TruckNav one instead, its subsidised by Renault to get their logo all over it, but is actually a 2011 updated CoPilot app, with far more features as its designed for professional drivers, and its 2/3rds of the price - result! You also get free Weather, updated POI's, speed cameras and traffic info for life. Which with TomTom etc I think you have to pay for?
It'd also be useful if you want to hire a Motorhome/RV thing, and it creates the routes based on vehicle type, as well as having a "walking mode" to get you to nearby ATM's, public toilets, shops etc.
Hope thats helpful to someone.
Alex