I used to like iTopoMaps but it kept crashing my iThings. Perhaps the November update will make it better, I'll try it again. More recently I've been using Motion-X GPS. It's decent but not great.



That is not the case. On the iPhone, GPS has its own receiver and as long as the satellites are working and you have a decent-enough view of the sky, you'll get a position fix. Data relies upon WiFi or cellular data. There are plenty of places where the GPS receiver will work but you won't be able to download map data on the fly.

Paper maps are good and I'm in favor of them. I use the GPS on my iPhone as a backup. In the backcountry, I mark important locations (campsite, trailhead, etc.) in my map app. After that I put the phone in airplane mode to conserve battery -- that way it won't keep trying to find a cellular signal. It's very quick to turn airplane mode off and get a position fix if I need one.