I'd get the most basic mapping GPS you can find, I've got a Garmin Etrex 20 and Iphone 4s. When it comes to hard core navigation, the Etrex is the winner by far. I find most people get lost navigating to the start of walks, put a track in the Garmin and you'll get there every time, providing the track is correct. I do a lot of cycle touring, while in Vietnam over Christmas, the only time I got lost was when I decided not to follow the GPS track and where I was no one spoke English.
The Garmin's a beast when it comes to custom mapping whereas the IPhone is a dream come true but battery life and lack of GPS ability are the only drawbacks I find.
When you buy a GPS, you'll find that you can do a lot more with it than you first intended so be prepared for a learning journey.
I'm off on a MTB ride now, the IPhone has the maps onboard while the Garmin is doing the track logging.