Bought a new iphone 4 and would like to know what is the best gps app

Bought a new iphone4 and want to use it on a trip to wa and afterwards use it when I go out prospecting. I downloaded the free mudmap app but can't work out what maps to buy as they have several different series including 4wd. Can anyone tell me more about this and what is the best app from experience.

Thanks

As a keen fisherman I use Navionics which is the best marine gps software u can buy and great on land

If you jailbreak your phone there are some great app's that will work on true GPS!(not cellular tower triangulation, like the native app and most in the app store) and totally off network!!!(downloaded maps are saved in your phone) if you don't want to jailbreak then the best app that I have found is ArcGIS, here in the USA i can get LR2000 to work on my iPhone and know exactly what claim I am on!!! I have not used it for navigation yet but i am in love with this app!

The native map app on the phone is almost worthless for navigation out of any city and is totally worthless at finding GPS points.

If you do decide to jailbreak then try out xGPS and ImgOsm they are great apps.