I know I'm in a minority but I have to say that I wasnt that impressed with the map display on my GPS III Pilot.
The moving map screen is almost so small as to be useless, and some of the map data is wrong, eg Cromarty Firth (If I remember correctly) is in the wrong place.
The screen that works like a VOR is very good, though, and I wouldnt dream of going any distance from base without having it with me so it must be doing a few things right.
Just make sure you see one for yourself before you buy is my advice. I've not used a Skymap unit in flight, but the map display looks better on its big screen.
The CAA maps on an iPaq look brilliant, but I'm not sure what functions are in there:routes, goto etc?
If you do decide to go for a III there there should be a lot of seconhand bargains about as people upgrade to the new Garmin.